141. The most important DDL statements in SQL are:
CREATE TABLE - creates a new database table
ALTER TABLE - alters (changes) a database table
DROP TABLE - deletes a database table
CREATE INDEX - creates an index (search key)
DROP INDEX - deletes an index
142. Operators used in SELECT statements.
= Equal
<> or != Not equal
> Greater than
<>= Greater than or equal
<= Less than or equal BETWEEN Between an inclusive range LIKE Search for a pattern
143. SELECT statements:
SELECT column_name(s) FROM table_name
SELECT DISTINCT column_name(s) FROM table_name
SELECT column FROM table WHERE column operator value
SELECT column FROM table WHERE column LIKE pattern
SELECT column,SUM(column) FROM table GROUP BY column
SELECT column,SUM(column) FROM table GROUP BY column HAVING SUM(column) condition value
Note that single quotes around text values and numeric values should not be enclosed in quotes. Double quotes may be acceptable
in some databases.
144. The SELECT INTO Statement is most often used to create backup copies of tables or for archiving records.
SELECT column_name(s) INTO newtable [IN externaldatabase] FROM source
SELECT column_name(s) INTO newtable [IN externaldatabase] FROM source WHERE column_name operator value
145. The INSERT INTO Statements:
INSERT INTO table_name VALUES (value1, value2,....)
INSERT INTO table_name (column1, column2,...) VALUES (value1, value2,....)
146. The Update Statement:
UPDATE table_name SET column_name = new_value WHERE column_name = some_value
147. The Delete Statements:
DELETE FROM table_name WHERE column_name = some_value
Delete All Rows:
DELETE FROM table_name or DELETE * FROM table_name
148. Sort the Rows:
SELECT column1, column2, ... FROM table_name ORDER BY columnX, columnY, ..
SELECT column1, column2, ... FROM table_name ORDER BY columnX DESC
SELECT column1, column2, ... FROM table_name ORDER BY columnX DESC, columnY ASC
149. The IN operator may be used if you know the exact value you want to return for at least one of the columns.
SELECT column_name FROM table_name WHERE column_name IN (value1,value2,..)
150. BETWEEN ... AND
SELECT column_name FROM table_name WHERE column_name BETWEEN value1 AND value2 The values can be numbers, text, or dates.
Saturday, March 29, 2008
FAQ - Database Testing (131 to 140)
131. How to know which index a table is using?
SELECT table_name,index_name FROM user_constraints
132. How to copy the tables, schema and views from one SQL server to another?
Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets user extract, transform, and consolidate data from disparate sources into single or multiple destinations.
133. What is Self Join?
This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company have a hierarchal reporting structure whereby one member of staff reports to another.
134. What is Cross Join?
A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
135. Which virtual table does a trigger use?
Inserted and Deleted.
136. List few advantages of Stored Procedure?
* Stored procedure can reduced network traffic and latency, boosting application performance.
* Stored procedure execution plans can be reused, staying cached in SQL Server's memory, reducing server overhead.
* Stored procedures help promote code reuse.
* Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
* Stored procedures provide better security to your data.
137. What is DataWarehousing?
* Subject-oriented, meaning that the data in the database is organized so that all the data elements relating to the same real-world event or object are linked together;
* Time-variant, meaning that the changes to the data in the database are tracked and recorded so that reports can be produced showing changes over time;
* Non-volatile, meaning that data in the database is never over-written or deleted, once committed, the data is static, read-only, but retained for future reporting;
* Integrated, meaning that the database contains data from most or all of an organization's operational applications, and that this data is made consistent.
138. What is OLTP (OnLine Transaction Processing)?
In OLTP - online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.
139. How do SQL server 2000 and XML linked? Can XML be used to access data?
FOR XML (ROW, AUTO, EXPLICIT)
You can execute SQL queries against existing relational databases to return results as XML rather than standard rowsets. These queries can be executed directly or from within stored procedures. To retrieve XML results, use the FOR XML clause of the SELECT statement and specify an XML mode of RAW, AUTO, or EXPLICIT.
OPENXML
OPENXML is a Transact-SQL keyword that provides a relational/rowset view over an in-memory XML document. OPENXML is a rowset provider similar to a table or a view. OPENXML provides a way to access XML data within the Transact-SQL context by transferring data from an XML document into the relational tables. Thus, OPENXML allows you to manage an XML document and its interaction with the relational environment.
140. What is an execution plan? When would you use it? How would you view the execution plan?
An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called "Show Execution Plan" (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.
SELECT table_name,index_name FROM user_constraints
132. How to copy the tables, schema and views from one SQL server to another?
Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of graphical tools and programmable objects that lets user extract, transform, and consolidate data from disparate sources into single or multiple destinations.
133. What is Self Join?
This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company have a hierarchal reporting structure whereby one member of staff reports to another.
134. What is Cross Join?
A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.
135. Which virtual table does a trigger use?
Inserted and Deleted.
136. List few advantages of Stored Procedure?
* Stored procedure can reduced network traffic and latency, boosting application performance.
* Stored procedure execution plans can be reused, staying cached in SQL Server's memory, reducing server overhead.
* Stored procedures help promote code reuse.
* Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
* Stored procedures provide better security to your data.
137. What is DataWarehousing?
* Subject-oriented, meaning that the data in the database is organized so that all the data elements relating to the same real-world event or object are linked together;
* Time-variant, meaning that the changes to the data in the database are tracked and recorded so that reports can be produced showing changes over time;
* Non-volatile, meaning that data in the database is never over-written or deleted, once committed, the data is static, read-only, but retained for future reporting;
* Integrated, meaning that the database contains data from most or all of an organization's operational applications, and that this data is made consistent.
138. What is OLTP (OnLine Transaction Processing)?
In OLTP - online transaction processing systems relational database design use the discipline of data modeling and generally follow the Codd rules of data normalization in order to ensure absolute data integrity. Using these rules complex information is broken down into its most simple structures (a table) where all of the individual atomic level elements relate to each other and satisfy the normalization rules.
139. How do SQL server 2000 and XML linked? Can XML be used to access data?
FOR XML (ROW, AUTO, EXPLICIT)
You can execute SQL queries against existing relational databases to return results as XML rather than standard rowsets. These queries can be executed directly or from within stored procedures. To retrieve XML results, use the FOR XML clause of the SELECT statement and specify an XML mode of RAW, AUTO, or EXPLICIT.
OPENXML
OPENXML is a Transact-SQL keyword that provides a relational/rowset view over an in-memory XML document. OPENXML is a rowset provider similar to a table or a view. OPENXML provides a way to access XML data within the Transact-SQL context by transferring data from an XML document into the relational tables. Thus, OPENXML allows you to manage an XML document and its interaction with the relational environment.
140. What is an execution plan? When would you use it? How would you view the execution plan?
An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called "Show Execution Plan" (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.
FAQ - Database Testing (121 to 130)
121. What are the properties of the Relational tables?
Relational tables have six properties:
Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.
122. What is De-normalization?
De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.
123. How to get @@error and @@rowcount at the same time?
If @@Rowcount is checked after Error checking statement then it will have 0 as the value of
@@Recordcount as it would have been reset.
And if @@Recordcount is checked before the error-checking statement then @@Error would get reset.
To get @@error and @@rowcount at the same time do both in same statement and store them in local variable. SELECT @RC = @@ROWCOUNT, @ER = @@ERROR
124. What is Identity?
Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set, but most DBA leave these at 1. A GUID column also generates numbers, the value of this cannot be controled. Identity/GUID columns do not need to be indexed.
125. What is a Scheduled Jobs or What is a Scheduled Tasks?
Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule administrative tasks, such as cube processing, to run during times of slow business activity. User can also determine the order in which tasks run by creating job steps within a SQL Server Agent job. E.g. Back up database, Update Stats of Tables. Job steps give user control over flow of execution. If one job fails, user can configure SQL Server Agent to continue to run the remaining tasks or to stop execution.
126. What is a table called, if it does not have neither Cluster nor Non-cluster Index? What is it used for?
Unindexed table or Heap. Microsoft Press Books and Book On Line (BOL) refers it as Heap.
A heap is a table that does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together. Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table and than do bulk of inserts and to restore those indexes after that.
127. What is BCP? When does it used?
BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination.
128. How do you load large data to the SQL server database?
BulkCopy is a tool used to copy huge amount of data from tables. BULK INSERT command helps to Imports a data file into a database table or view in a user-specified format.
129. Can we rewrite subqueries into simple select statements or with joins?
Subqueries can often be re-written to use a standard outer join, resulting in faster performance. As we may know, an outer join uses the plus sign (+) operator to tell the database to return all non-matching rows with NULL values. Hence we combine the outer join with a NULL test in the WHERE clause to reproduce the result set without using a sub-query.
130. Can SQL Servers linked to other servers like Oracle?
SQL Server can be lined to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle has a OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL Server group.
Relational tables have six properties:
Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.
122. What is De-normalization?
De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.
123. How to get @@error and @@rowcount at the same time?
If @@Rowcount is checked after Error checking statement then it will have 0 as the value of
@@Recordcount as it would have been reset.
And if @@Recordcount is checked before the error-checking statement then @@Error would get reset.
To get @@error and @@rowcount at the same time do both in same statement and store them in local variable. SELECT @RC = @@ROWCOUNT, @ER = @@ERROR
124. What is Identity?
Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set, but most DBA leave these at 1. A GUID column also generates numbers, the value of this cannot be controled. Identity/GUID columns do not need to be indexed.
125. What is a Scheduled Jobs or What is a Scheduled Tasks?
Scheduled tasks let user automate processes that run on regular or predictable cycles. User can schedule administrative tasks, such as cube processing, to run during times of slow business activity. User can also determine the order in which tasks run by creating job steps within a SQL Server Agent job. E.g. Back up database, Update Stats of Tables. Job steps give user control over flow of execution. If one job fails, user can configure SQL Server Agent to continue to run the remaining tasks or to stop execution.
126. What is a table called, if it does not have neither Cluster nor Non-cluster Index? What is it used for?
Unindexed table or Heap. Microsoft Press Books and Book On Line (BOL) refers it as Heap.
A heap is a table that does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together. Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table and than do bulk of inserts and to restore those indexes after that.
127. What is BCP? When does it used?
BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination.
128. How do you load large data to the SQL server database?
BulkCopy is a tool used to copy huge amount of data from tables. BULK INSERT command helps to Imports a data file into a database table or view in a user-specified format.
129. Can we rewrite subqueries into simple select statements or with joins?
Subqueries can often be re-written to use a standard outer join, resulting in faster performance. As we may know, an outer join uses the plus sign (+) operator to tell the database to return all non-matching rows with NULL values. Hence we combine the outer join with a NULL test in the WHERE clause to reproduce the result set without using a sub-query.
130. Can SQL Servers linked to other servers like Oracle?
SQL Server can be lined to any server provided it has OLE-DB provider from Microsoft to allow a link. E.g. Oracle has a OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL Server group.
FAQ - Database Testing (111 to 120)
111. What are the different types of replication? Explain.
The SQL Server 2000-supported replication types are as follows:
· Transactional
· Snapshot
· Merge
Snapshot replication distributes data exactly as it appears at a specific moment in time and does not monitor for updates to the data. Snapshot replication is best used as a method for replicating data that changes infrequently or where the most up-to-date values (low latency) are not a requirement. When synchronization occurs, the entire snapshot is generated and sent to Subscribers.
Transactional replication, an initial snapshot of data is applied at Subscribers, and then when data modifications are made at the Publisher, the individual transactions are captured and propagated to Subscribers.
Merge replication is the process of distributing data from Publisher to Subscribers, allowing the Publisher and Subscribers to make updates while connected or disconnected, and then merging the updates between sites when they are connected.
112. What are the OS services that the SQL Server installation adds?
MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)
113. What are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.
114. What does it mean to have quoted_identifier on? What are the implications of having it off?
When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all Transact-SQL rules for identifiers.
115. What is the STUFF function and how does it differ from the REPLACE function?
STUFF function to overwrite existing characters. Using this syntax, STUFF(string_expression, start, length, replacement_characters), string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string.
REPLACE function to replace existing characters of all occurance. Using this syntax
REPLACE(string_expression, search_string, replacement_string), where every incidence of
search_string found in the string_expression will be replaced with replacement_string.
116. Using query analyzer, name 3 ways to get an accurate count of the number of records in a table?
SELECT * FROM table1
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid <>
117. How to rebuild Master Database?
Shutdown Microsoft SQL Server 2000, and then run Rebuildm.exe. This is located in the Program Files\Microsoft SQL Server\80\Tools\Binn directory.
In the Rebuild Master dialog box, click Browse.
In the Browse for Folder dialog box, select the \Data folder on the SQL Server 2000 compact disc or in the shared network directory from which SQL Server 2000 was installed, and then click OK.
Click Settings.
In the Collation Settings dialog box, verify or change settings used for the master database and all other databases. Initially, the default collation settings are shown, but these may not match the collation selected during setup. You can select the same settings used during setup or select new collation settings. When done,
click OK.
In the Rebuild Master dialog box, click Rebuild to start the process.
The Rebuild Master utility reinstalls the master database.
To continue, you may need to stop a server that is running.
Source: http://msdn2.microsoft.com/en-us/library/aa197950(SQL.80).aspx
118. What is the basic functions for master, msdb, model, tempdb databases?
The Master database holds information for all databases located on the SQL Server instance and is the glue that holds the engine together. Because SQL Server cannot start without a functioning master database, you must administer this database with care. The msdb database stores information regarding database backups, SQL Agent information, DTS
packages, SQL Server jobs, and some replication information such as for log shipping.
The tempdb holds temporary objects such as global and local temporary tables and stored procedures. The model is essentially a template database used in the creation of any new user database created in the instance.
119. What are primary keys and foreign keys?
Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.
Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.
120. What is data integrity? Explain constraints?
Data integrity is an important feature in SQL Server. When used properly, it ensures that data is accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.
A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.
A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.
A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.
A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.
A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.
The SQL Server 2000-supported replication types are as follows:
· Transactional
· Snapshot
· Merge
Snapshot replication distributes data exactly as it appears at a specific moment in time and does not monitor for updates to the data. Snapshot replication is best used as a method for replicating data that changes infrequently or where the most up-to-date values (low latency) are not a requirement. When synchronization occurs, the entire snapshot is generated and sent to Subscribers.
Transactional replication, an initial snapshot of data is applied at Subscribers, and then when data modifications are made at the Publisher, the individual transactions are captured and propagated to Subscribers.
Merge replication is the process of distributing data from Publisher to Subscribers, allowing the Publisher and Subscribers to make updates while connected or disconnected, and then merging the updates between sites when they are connected.
112. What are the OS services that the SQL Server installation adds?
MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)
113. What are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.
114. What does it mean to have quoted_identifier on? What are the implications of having it off?
When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers cannot be quoted and must follow all Transact-SQL rules for identifiers.
115. What is the STUFF function and how does it differ from the REPLACE function?
STUFF function to overwrite existing characters. Using this syntax, STUFF(string_expression, start, length, replacement_characters), string_expression is the string that will have characters substituted, start is the starting position, length is the number of characters in the string that are substituted, and replacement_characters are the new characters interjected into the string.
REPLACE function to replace existing characters of all occurance. Using this syntax
REPLACE(string_expression, search_string, replacement_string), where every incidence of
search_string found in the string_expression will be replaced with replacement_string.
116. Using query analyzer, name 3 ways to get an accurate count of the number of records in a table?
SELECT * FROM table1
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid <>
117. How to rebuild Master Database?
Shutdown Microsoft SQL Server 2000, and then run Rebuildm.exe. This is located in the Program Files\Microsoft SQL Server\80\Tools\Binn directory.
In the Rebuild Master dialog box, click Browse.
In the Browse for Folder dialog box, select the \Data folder on the SQL Server 2000 compact disc or in the shared network directory from which SQL Server 2000 was installed, and then click OK.
Click Settings.
In the Collation Settings dialog box, verify or change settings used for the master database and all other databases. Initially, the default collation settings are shown, but these may not match the collation selected during setup. You can select the same settings used during setup or select new collation settings. When done,
click OK.
In the Rebuild Master dialog box, click Rebuild to start the process.
The Rebuild Master utility reinstalls the master database.
To continue, you may need to stop a server that is running.
Source: http://msdn2.microsoft.com/en-us/library/aa197950(SQL.80).aspx
118. What is the basic functions for master, msdb, model, tempdb databases?
The Master database holds information for all databases located on the SQL Server instance and is the glue that holds the engine together. Because SQL Server cannot start without a functioning master database, you must administer this database with care. The msdb database stores information regarding database backups, SQL Agent information, DTS
packages, SQL Server jobs, and some replication information such as for log shipping.
The tempdb holds temporary objects such as global and local temporary tables and stored procedures. The model is essentially a template database used in the creation of any new user database created in the instance.
119. What are primary keys and foreign keys?
Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.
Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.
120. What is data integrity? Explain constraints?
Data integrity is an important feature in SQL Server. When used properly, it ensures that data is accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.
A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.
A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.
A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.
A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.
A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.
FAQ - Database Testing (101 to 110)
101. What are the authentication modes in SQL Server? How can it be changed?
Windows mode and mixed mode (SQL & Windows).
To change authentication mode in SQL Server click Start, Programs, Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group.
Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the Security page.
102. Where are SQL server users names and passwords are stored in sql server?
They get stored in master db in the sysxlogins table.
Which command using Query Analyzer will give you the version of SQL server and operating
system?
SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')
103. What is SQL server agent?
SQL Server agent plays an important role in the day-to-day tasks of a database dministrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full-function scheduling engine, which allows you to schedule your own jobs and scripts.
104. Can a stored procedure call itself or recursive stored procedure? How many level SP nesting possible?
Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps.
Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code references up to 32 levels.
105. What is @@ERROR?
The @@ERROR automatic variable returns the error code of the last Transact-SQL statement. If there was no error, @@ERROR returns zero. Because @@ERROR is reset after each Transact-SQL statement, it must be saved to a variable if it is needed to process it further after checking it.
106. What is Raise error?
Stored procedures report errors to client applications via the RAISERROR command. RAISERROR doesn't change the flow of a procedure; it merely displays an error message, sets the @@ERROR automatic variable, and optionally writes the message to the SQL Server error log and the NT application event log.
107. What is log shipping?
Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db can be used this as the Disaster Recovery plan. The key feature of log shipping is that is will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.
108. What is the difference between a local and a global variable?
A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement. A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connection are closed, the data in the global temporary table disappears. However,
the table definition remains with the database for access when database is opened next time.
109. What command do we use to rename a db?
sp_renamedb ‘oldname’ , ‘newname’
If someone is using db it will not accept sp_renmaedb. In that case first bring db to single user using sp_dboptions. Use sp_renamedb to rename database. Use sp_dboptions to bring database to multi user mode.
110. What is sp_configure commands and set commands?
Use sp_configure to display or change server-level settings. To change database-level settings, use ALTER DATABASE. To change settings that affect only the current user session, use the SET statement.
Windows mode and mixed mode (SQL & Windows).
To change authentication mode in SQL Server click Start, Programs, Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group.
Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the Security page.
102. Where are SQL server users names and passwords are stored in sql server?
They get stored in master db in the sysxlogins table.
Which command using Query Analyzer will give you the version of SQL server and operating
system?
SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')
103. What is SQL server agent?
SQL Server agent plays an important role in the day-to-day tasks of a database dministrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full-function scheduling engine, which allows you to schedule your own jobs and scripts.
104. Can a stored procedure call itself or recursive stored procedure? How many level SP nesting possible?
Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps.
Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code references up to 32 levels.
105. What is @@ERROR?
The @@ERROR automatic variable returns the error code of the last Transact-SQL statement. If there was no error, @@ERROR returns zero. Because @@ERROR is reset after each Transact-SQL statement, it must be saved to a variable if it is needed to process it further after checking it.
106. What is Raise error?
Stored procedures report errors to client applications via the RAISERROR command. RAISERROR doesn't change the flow of a procedure; it merely displays an error message, sets the @@ERROR automatic variable, and optionally writes the message to the SQL Server error log and the NT application event log.
107. What is log shipping?
Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db can be used this as the Disaster Recovery plan. The key feature of log shipping is that is will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.
108. What is the difference between a local and a global variable?
A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement. A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connection are closed, the data in the global temporary table disappears. However,
the table definition remains with the database for access when database is opened next time.
109. What command do we use to rename a db?
sp_renamedb ‘oldname’ , ‘newname’
If someone is using db it will not accept sp_renmaedb. In that case first bring db to single user using sp_dboptions. Use sp_renamedb to rename database. Use sp_dboptions to bring database to multi user mode.
110. What is sp_configure commands and set commands?
Use sp_configure to display or change server-level settings. To change database-level settings, use ALTER DATABASE. To change settings that affect only the current user session, use the SET statement.
FAQ - Database Testing (91 to 100)
91. Difference between Function and Stored Procedure?
UDF(User Defined Function) can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored procedures cannot be.
UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables. Inline UDF's can be though of as views that take parameters and can be used in JOINs and other Rowset operations.
92. When is the use of UPDATE_STATISTICS command?
This command is basically used when a large processing of data has occurred. If a large amount of deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.
93. What types of Joins are possible with SQL Server?
Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.
94. What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
Specifies a search condition for a group or an aggregate. HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.
95. What is sub-query? Explain properties of sub-query.
Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A sub-query is executed by enclosing it in a set of parentheses. Sub-queries are generally used to return a single row as an atomic value, though they may be used to compare values against multiple rows with the IN keyword.
A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a result set. Meaning a subquery SELECT statement can standalone and is not depended on the statement in which it is nested. A subquery SELECT statement can return any number of values, and can be found in, the column list of a SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A Subquery can also be used as a parameter to a function call. Basically a subquery can be used anywhere an expression can be used.
Properties of Sub-Query
A subquery must be enclosed in the parenthesis.
A subquery must be put in the right hand of the comparison operator, and
A subquery cannot contain a ORDER-BY clause.
A query can contain more than one sub-queries.
96. What are types of sub-queries?
Single-row subquery, where the subquery returns only one row.
Multiple-row subquery, where the subquery returns multiple rows,.and
Multiple column subquery, where the subquery returns multiple columns.
97. What is SQL Profiler?
SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performance by executing too slowly. Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.
98. What is User Defined Functions?
User-Defined Functions allow to define its own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.
99. What kind of User-Defined Functions can be created?
There are three types of User-Defined functions in SQL Server 2000 and they are Scalar, Inline Table- Valued and Multi-statement Table-valued.
Scalar User-Defined Function
A Scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages. You pass in 0 to many parameters and you get a return value.
Inline Table-Value User-Defined Function
An Inline Table-Value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-updateable view of the underlying tables.
Multi-statement Table-Value User-Defined Function
A Multi-Statement Table-Value user-defined function returns a table and is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a TSQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior found when using a stored procedure which can also return record sets.
100. Which TCP/IP port does SQL Server run on? How can it be changed?
SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties –> Port number.both on client and the server.
UDF(User Defined Function) can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored procedures cannot be.
UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables. Inline UDF's can be though of as views that take parameters and can be used in JOINs and other Rowset operations.
92. When is the use of UPDATE_STATISTICS command?
This command is basically used when a large processing of data has occurred. If a large amount of deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to take these changes into account. UPDATE_STATISTICS updates the indexes on these tables accordingly.
93. What types of Joins are possible with SQL Server?
Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.
94. What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
Specifies a search condition for a group or an aggregate. HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.
95. What is sub-query? Explain properties of sub-query.
Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A sub-query is executed by enclosing it in a set of parentheses. Sub-queries are generally used to return a single row as an atomic value, though they may be used to compare values against multiple rows with the IN keyword.
A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a result set. Meaning a subquery SELECT statement can standalone and is not depended on the statement in which it is nested. A subquery SELECT statement can return any number of values, and can be found in, the column list of a SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A Subquery can also be used as a parameter to a function call. Basically a subquery can be used anywhere an expression can be used.
Properties of Sub-Query
A subquery must be enclosed in the parenthesis.
A subquery must be put in the right hand of the comparison operator, and
A subquery cannot contain a ORDER-BY clause.
A query can contain more than one sub-queries.
96. What are types of sub-queries?
Single-row subquery, where the subquery returns only one row.
Multiple-row subquery, where the subquery returns multiple rows,.and
Multiple column subquery, where the subquery returns multiple columns.
97. What is SQL Profiler?
SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performance by executing too slowly. Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.
98. What is User Defined Functions?
User-Defined Functions allow to define its own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.
99. What kind of User-Defined Functions can be created?
There are three types of User-Defined functions in SQL Server 2000 and they are Scalar, Inline Table- Valued and Multi-statement Table-valued.
Scalar User-Defined Function
A Scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages. You pass in 0 to many parameters and you get a return value.
Inline Table-Value User-Defined Function
An Inline Table-Value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-updateable view of the underlying tables.
Multi-statement Table-Value User-Defined Function
A Multi-Statement Table-Value user-defined function returns a table and is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a TSQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior found when using a stored procedure which can also return record sets.
100. Which TCP/IP port does SQL Server run on? How can it be changed?
SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties –> Port number.both on client and the server.
FAQ - Database Testing ( 81 to 90 )
81. What are the different index configurations a table can have?
A table can have one of the following index configurations:
No indexes
A clustered index
A clustered index and many non-clustered indexes
A non-clustered index
Many non-clustered indexes
82. What is cursor?
Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time. In order to work with a cursor we need to perform some steps in the following order:
Declare cursor
Open cursor
Fetch row from the cursor
Process fetched row
Close cursor
Deallocate cursor
83. What is the use of DBCC commands?
DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.
E.g. DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.
DBCC CHECKALLOC - To check that all pages in a db are correctly allocated.
DBCC CHECKFILEGROUP - Checks all tables file group for any damage.
84. What is a Linked Server?
Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements. With a linked server, you can create very clean, easy to follow, SQL statements that allow remote data to be retrieved, joined and combined with local data. Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.
85. What is Collation?
Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence, with options for specifying case sensitivity, accent marks, kana character types and character width.
86. What are different types of Collation Sensitivity?
Case sensitivity
A and a, B and b, etc.
Accent sensitivity
a and á, o and ó, etc.
Kana Sensitivity
When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana
sensitive.
Width sensitivity
When a single-byte character (half-width) and the same character when represented as a double-byte
character (full-width) are treated differently then it is width sensitive.
87. What's the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a non-clustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.
88. How to implement one-to-one, one-to-many and many-to-many relationships while designing tables ?
One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.
One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.
Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.
89. What is a NOLOCK?
Using the NOLOCK query optimizer hint is generally considered good practice in order to improve concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are taken when data is read. The result is a Dirty Read, which means that another process could be updating the data at the exact time you are reading it. There are no guarantees that your query will retrieve the most recent data. The advantage to performance is that your reading of data will not block updates from taking place, and updates will not block your reading of data. SELECT statements take Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but
other processes are blocked from modifying the data. The updates will queue until all the reads have completed, and reads requested after the update will wait for the updates to complete. The result to your system is delay(blocking).
90. What is difference between DELETE & TRUNCATE commands?
Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.
TRUNCATE
TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.
TRUNCATE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column.
You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint.
Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
TRUNCATE can not be Rolled back.
TRUNCATE is DDL Command.
TRUNCATE Resets identity of the table.
DELETE
DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.
DELETE Can be used with or without a WHERE clause
DELETE Activates Triggers.
DELETE Can be Rolled back.
DELETE is DML Command.
DELETE does not reset identity of the table.
A table can have one of the following index configurations:
No indexes
A clustered index
A clustered index and many non-clustered indexes
A non-clustered index
Many non-clustered indexes
82. What is cursor?
Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time. In order to work with a cursor we need to perform some steps in the following order:
Declare cursor
Open cursor
Fetch row from the cursor
Process fetched row
Close cursor
Deallocate cursor
83. What is the use of DBCC commands?
DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.
E.g. DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.
DBCC CHECKALLOC - To check that all pages in a db are correctly allocated.
DBCC CHECKFILEGROUP - Checks all tables file group for any damage.
84. What is a Linked Server?
Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements. With a linked server, you can create very clean, easy to follow, SQL statements that allow remote data to be retrieved, joined and combined with local data. Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.
85. What is Collation?
Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence, with options for specifying case sensitivity, accent marks, kana character types and character width.
86. What are different types of Collation Sensitivity?
Case sensitivity
A and a, B and b, etc.
Accent sensitivity
a and á, o and ó, etc.
Kana Sensitivity
When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana
sensitive.
Width sensitivity
When a single-byte character (half-width) and the same character when represented as a double-byte
character (full-width) are treated differently then it is width sensitive.
87. What's the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a non-clustered index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key allows one NULL only.
88. How to implement one-to-one, one-to-many and many-to-many relationships while designing tables ?
One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.
One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.
Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.
89. What is a NOLOCK?
Using the NOLOCK query optimizer hint is generally considered good practice in order to improve concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are taken when data is read. The result is a Dirty Read, which means that another process could be updating the data at the exact time you are reading it. There are no guarantees that your query will retrieve the most recent data. The advantage to performance is that your reading of data will not block updates from taking place, and updates will not block your reading of data. SELECT statements take Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but
other processes are blocked from modifying the data. The updates will queue until all the reads have completed, and reads requested after the update will wait for the updates to complete. The result to your system is delay(blocking).
90. What is difference between DELETE & TRUNCATE commands?
Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.
TRUNCATE
TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.
TRUNCATE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column.
You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint.
Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
TRUNCATE can not be Rolled back.
TRUNCATE is DDL Command.
TRUNCATE Resets identity of the table.
DELETE
DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.
DELETE Can be used with or without a WHERE clause
DELETE Activates Triggers.
DELETE Can be Rolled back.
DELETE is DML Command.
DELETE does not reset identity of the table.
FAQ - Database Testing ( 71 to 80 )
71. What is the difference between ORACLE, SQL, and SQL SERVER?
Oracle is based on RDBMS.SQL is Structured Query Language.SQL Server is another tool for RDBMS provided by Microsoft.
72. How to retrieving the data from 11th column to nth column in a table?
SELECT * FROM EMP WHERE ROWID IN ( SELECT ROWID FROM EMP WHERE ROWNUM <=&UPTOMINUSSELECT ROWID FROM EMP WHERE ROWNUM <&STARTFROM)from this you can select between any range.
73. Difference between decode and case. In which case we are using case and in which case we are using decode? Explain with an example?
First I will give one example using 'decode'SQL>SELECT ENAME, SAL, DECODE (DEPTNO, 10, 'ACCOUNTING', 20,'RESEARCH', 30,'SALES', 40,'OPERATIONS','OTHERS') "DEPARTMENTS" FROM EMP;
I have used the decode function on 'deptno' column. It will give the user-friendly output. instead of using 'accounting', ‘research’. We can use anything we want to get the friendly outputs.
I have to check-out the 'case' function after that I will give an example using CASE expression we can use all comparative operators (<, >, ==, etc), where as using DECODE we should always use = condition.
74. What is the main difference between the IN and EXISTS clause in sub-queries?
The main difference between the IN and EXISTS predicate in sub-query is the way in which the query gets executed.IN -- The inner query is executed first and the list of values obtained as its result is used by the outer query. The inner query is executed for only once.EXISTS -- The first row from the outer query is selected, then the inner query is executed and , the outer query output uses this result for checking. This process of inner query execution repeats as many no. of times as there are outer query rows. That is, if there are ten rows that can result from outer query, the inner query is executed that many no. of times.
75. Difference between an equi-join and union?
Indeed both equi join and the Union are very different. Equi join is used to establish a condition between two tables to select data from them.. eg SELECT A.EMPLOYEEID, A.EMPLOYEENAME, B.DEPT_NAME FROM EMPLOYEEMASTER A , DEPARTMENTMASTER BWHERE A.EMPLOYEEID = B.EMPLOYEEID;This is the example of equijoin whereas with a Union allows you to select the similar data based on different conditions egSELECT A.EMPLOYEEID, A.EMPLOYEENAME FROM EMPLOYEEMASTER A WHERE A.EMPLOYEEID >100 B.EMPLOYEEIDUNION
SELECT A.EMPLOYEEID, A.EMPLOYEENAME FROM EMPLOYEEMASTER A WHERE A.EMPLOYEENAME LIKE 'B%'the above is the example of Union where in we select employee name and Id for two different conditions into the same record set and is used thereafter.
76. How to find out the database name from SQL*PLUS command prompt?
SELECT * FROM GLOBAL_NAME;This will give the database name which you are currently connected to.
77. What is the difference between Single row sub-Query and Scalar sub-Query?
Single row sub-query returns a value that is used by where clause, whereas scalar sub-query is a select statement used in column list can be thought of as an inline function in select column list.
78. What is View?
A simple view can be thought of as a subset of a table. It can be used for retrieving data, as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted in the table the view was created with. It should also be noted that as data in the original table changes, so does data in the view, as views are the way to look at part of the original table. The results of using a view are not permanently stored in the database. The data accessed through a view is actually constructed using standard T-SQL select command and can come from one to many different base tables or even other views.
79. What is Index?
An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes, they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.
Clustered indexes define the physical sorting of a database table’s rows in the storage media. For this reason, each database table may have only one clustered index.
Non-clustered indexes are created outside of the database table and contain a sorted list of references to the table itself.
80. What are the difference between clustered and a non-clustered index?
A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A non-clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a non-clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.
FAQ - Database Testing ( 61 to 70 )
61. Can we call user-defined packages in SQL statements?
I do not agree that we can't call user- defined packages in the SQL statements. Instead we can call user defined packaged functions in the SELECT statement.
e.g. SELECT pkg.test(10) FROM DUAL;
62. What is table space?
Table-space is a physical concept. It has pages where the record of the database is stored with a logical perception of tables. So table space contains tables.
63. Explain normalization with examples?
Normalization is a process of eliminating the redundancy and increasing the integrity.
64. Given an unnormalized table with columns?
The query will be:
DELETE FROM TABNAME WHERE ROWID NOT IN (SELECT MAX (ROWID) FROM TABNAME GROUP BY NAME;
Here tabname is the table name
65. What is Reference cursor?
Reference cursor is dynamic cursor used with SQL statement like For select* from emp;
66. What is the difference between SQL and SQL Server?
SQLServer is an RDBMS just like oracle, DB2 from Microsoft whereas Structured Query Language (SQL), pronounced "sequel", is a language that provides an interface to relational database systems. IBM developed it in the 1970s for use in System R. SQL is a de facto standard, as well as an ISO and ANSI standard. SQL is used to perform various operations on RDBMS.
67. Difference between Store Procedure and Trigger?
Information related to Stored procedure you can see in,
USER_SOURCE, USER_OBJECTS (current user) tables
Information related to triggers stored in USER_SOURCE,USER_TRIGGERS (current user) Tables.Stored procedure can't be inactive but trigger can be Inactive.
68. I have a table with duplicate names in it. Write me a query which returns only duplicate rows with number of times they are repeated?
SELECT COL1 FROM TAB1 WHERE COL1 IN (SELECT MAX (COL1) FROM TAB1 GROUP BY COL1 HAVING COUNT (COL1) > 1 )
69. What is cluster? What is cluster index & non-cluster index?
Clustered Index: - A Clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table may have only one clustered index. Non-Non-Non-Clustered Index:- A Non-Clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows in the disk. The leaf nodes of a non-clustered index do not consists of the data pages. Instead the leaf node contains index rows.
70. What is Trigger?
A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.
I do not agree that we can't call user- defined packages in the SQL statements. Instead we can call user defined packaged functions in the SELECT statement.
e.g. SELECT pkg.test(10) FROM DUAL;
62. What is table space?
Table-space is a physical concept. It has pages where the record of the database is stored with a logical perception of tables. So table space contains tables.
63. Explain normalization with examples?
Normalization is a process of eliminating the redundancy and increasing the integrity.
64. Given an unnormalized table with columns?
The query will be:
DELETE FROM TABNAME WHERE ROWID NOT IN (SELECT MAX (ROWID) FROM TABNAME GROUP BY NAME;
Here tabname is the table name
65. What is Reference cursor?
Reference cursor is dynamic cursor used with SQL statement like For select* from emp;
66. What is the difference between SQL and SQL Server?
SQLServer is an RDBMS just like oracle, DB2 from Microsoft whereas Structured Query Language (SQL), pronounced "sequel", is a language that provides an interface to relational database systems. IBM developed it in the 1970s for use in System R. SQL is a de facto standard, as well as an ISO and ANSI standard. SQL is used to perform various operations on RDBMS.
67. Difference between Store Procedure and Trigger?
Information related to Stored procedure you can see in,
USER_SOURCE, USER_OBJECTS (current user) tables
Information related to triggers stored in USER_SOURCE,USER_TRIGGERS (current user) Tables.Stored procedure can't be inactive but trigger can be Inactive.
68. I have a table with duplicate names in it. Write me a query which returns only duplicate rows with number of times they are repeated?
SELECT COL1 FROM TAB1 WHERE COL1 IN (SELECT MAX (COL1) FROM TAB1 GROUP BY COL1 HAVING COUNT (COL1) > 1 )
69. What is cluster? What is cluster index & non-cluster index?
Clustered Index: - A Clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table may have only one clustered index. Non-Non-Non-Clustered Index:- A Non-Clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows in the disk. The leaf nodes of a non-clustered index do not consists of the data pages. Instead the leaf node contains index rows.
70. What is Trigger?
A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.
FAQ - Database Testing ( 51 to 60 )
51. What is difference between Oracle & MS Access? What are the disadvantages in Oracle and MS Access? What are features in Oracle and MS Access?
Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle.
52. What will be the output of the following query? SELECT DECODE (TRANSLATE (‘A’,’1234567890’,’1111111111’), '1','YES', ‘NO’);?
No.
Explanation:
The query checks whether a given string is a numerical digit.
53. Given an employee and manager table, write a SQL syntax that could be used to find out an employee's manager's manager, assuming all managers are in the employee table?
It is assumed that u have created a single table for populating data of Employee and Manager (.a Manager is also an Employee so s/he will be residing in the same table).The sample data would be like thisEmployeeID ----- EmployeeName ------- ManagerID1 Akhtar 02 Bilal 13 Faheem 2** This query will return "Akhtar" for given EmployeeID = 3.SELECT m.EmployeeName FROM #EmpTemp m WHERE m.EmloyeeID = (SELECT e.ManagerID FROM #EmpTemp e WHERE e.EmloyeeID = (Select t.ManagerID FROM #EmpTemp t WHERE t.EmloyeeID = 3))** This is solution is workable in case of 3-levels only not even to 2-levels of hierarchy. An n-level solution can be achieved by writing a Recursive stored procedure and that will also be given soon.
The best query is to create the dummy table and then make the relations,SELECT EMP.EMPLOYEEID, EMP.EMPLOYEENAME, EMP.MANAGERID,EMPTEMP.EMPLOYEENAME MANAGERFROM EMPLOYEES EMP ,EMPLOYEES EMPTEMPWHERE EMP.MANAGERID=EMPTEMP.EMPLOYEEID
54. When using COUNT (DISTINCT) is it better to use a self-join or temp table to find redundant data, and provide an example?
Instead of this we can use GROUP BY Clause with HAVING condition.For ex,SELECT COUNT(*),LASTNAME FROM TBLUSERS GROUP BY LASTNAME HAVING COUNT(*)>1This query return the duplicated lastnames values in the lastname column from tblUsers table.
55. What are the advantages and disadvantages of primary key and foreign key in SQL?
Primary key
Advantages
1) It is a unique key on which all the other candidate keys are functionally dependent
Disadvantage
1) There can be more than one keys on which all the other attributes are dependent on.
Foreign Key
Advantage
1) It allows referencing another table using the primary key for the other table.
56. What is difference between Co-related sub query and nested sub query?
Correlated sub-query runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query.
Nested sub-query runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row.For example, Correlated Sub-query: SELECT E1.EMPNAME, E1.BASICSAL, E1.DEPTNO FROM EMP E1 WHERE E1.BASICSAL = (SELECT MAX (BASICSAL) FROM EMP E2 WHERE E2.DEPTNO = E1.DEPTNO)Nested Sub-query: SELECT EMPNAME, BASICSAL, DEPTNO FROM EMP WHERE (DEPTNO, BASICSAL) IN (SELECT DEPTNO, MAX(BASICSAL) FROM EMP GROUP BY DEPTNO)
57. What is the back end processes when we type "SELECT * FROM TABLE"?
First it will look into the System Global Area (SGA) weather the query is been executed earlier. If it exists, it would retrieve the same output present in memory. If not the query we typed is complied and the resulting parse tree and execution plan is been stored in SGA. Then query gets executed and output is given to the application.
58. What is a Cursor?
To retrieve data with SQL one row at a time you need to use cursor processing. Not all relational databases support this, but many do. Here I show this in Oracle with PL/SQL, which is Procedural Language SQL. Cursor processing is done in several steps:1. Define the rows you want to retrieve. This is called declaring the cursor.2. Open the cursor. This activates the cursor and loads the data. Note that declaring the cursor doesn't load data, opening the cursor does.3. Fetch the data into variables.4. Close the cursor.
59. What is Stored Procedure?
A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database. e.g. sp_helpdb, sp_renamedb, sp_depends etc.
60. How do I write a cron, which will run a SQL query and mail the results to a group?
Use DBMS_JOB for scheduling a cron job and DBMS_MAIL to send the results through email.
Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle.
52. What will be the output of the following query? SELECT DECODE (TRANSLATE (‘A’,’1234567890’,’1111111111’), '1','YES', ‘NO’);?
No.
Explanation:
The query checks whether a given string is a numerical digit.
53. Given an employee and manager table, write a SQL syntax that could be used to find out an employee's manager's manager, assuming all managers are in the employee table?
It is assumed that u have created a single table for populating data of Employee and Manager (.a Manager is also an Employee so s/he will be residing in the same table).The sample data would be like thisEmployeeID ----- EmployeeName ------- ManagerID1 Akhtar 02 Bilal 13 Faheem 2** This query will return "Akhtar" for given EmployeeID = 3.SELECT m.EmployeeName FROM #EmpTemp m WHERE m.EmloyeeID = (SELECT e.ManagerID FROM #EmpTemp e WHERE e.EmloyeeID = (Select t.ManagerID FROM #EmpTemp t WHERE t.EmloyeeID = 3))** This is solution is workable in case of 3-levels only not even to 2-levels of hierarchy. An n-level solution can be achieved by writing a Recursive stored procedure and that will also be given soon.
The best query is to create the dummy table and then make the relations,SELECT EMP.EMPLOYEEID, EMP.EMPLOYEENAME, EMP.MANAGERID,EMPTEMP.EMPLOYEENAME MANAGERFROM EMPLOYEES EMP ,EMPLOYEES EMPTEMPWHERE EMP.MANAGERID=EMPTEMP.EMPLOYEEID
54. When using COUNT (DISTINCT) is it better to use a self-join or temp table to find redundant data, and provide an example?
Instead of this we can use GROUP BY Clause with HAVING condition.For ex,SELECT COUNT(*),LASTNAME FROM TBLUSERS GROUP BY LASTNAME HAVING COUNT(*)>1This query return the duplicated lastnames values in the lastname column from tblUsers table.
55. What are the advantages and disadvantages of primary key and foreign key in SQL?
Primary key
Advantages
1) It is a unique key on which all the other candidate keys are functionally dependent
Disadvantage
1) There can be more than one keys on which all the other attributes are dependent on.
Foreign Key
Advantage
1) It allows referencing another table using the primary key for the other table.
56. What is difference between Co-related sub query and nested sub query?
Correlated sub-query runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query.
Nested sub-query runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row.For example, Correlated Sub-query: SELECT E1.EMPNAME, E1.BASICSAL, E1.DEPTNO FROM EMP E1 WHERE E1.BASICSAL = (SELECT MAX (BASICSAL) FROM EMP E2 WHERE E2.DEPTNO = E1.DEPTNO)Nested Sub-query: SELECT EMPNAME, BASICSAL, DEPTNO FROM EMP WHERE (DEPTNO, BASICSAL) IN (SELECT DEPTNO, MAX(BASICSAL) FROM EMP GROUP BY DEPTNO)
57. What is the back end processes when we type "SELECT * FROM TABLE"?
First it will look into the System Global Area (SGA) weather the query is been executed earlier. If it exists, it would retrieve the same output present in memory. If not the query we typed is complied and the resulting parse tree and execution plan is been stored in SGA. Then query gets executed and output is given to the application.
58. What is a Cursor?
To retrieve data with SQL one row at a time you need to use cursor processing. Not all relational databases support this, but many do. Here I show this in Oracle with PL/SQL, which is Procedural Language SQL. Cursor processing is done in several steps:1. Define the rows you want to retrieve. This is called declaring the cursor.2. Open the cursor. This activates the cursor and loads the data. Note that declaring the cursor doesn't load data, opening the cursor does.3. Fetch the data into variables.4. Close the cursor.
59. What is Stored Procedure?
A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database. e.g. sp_helpdb, sp_renamedb, sp_depends etc.
60. How do I write a cron, which will run a SQL query and mail the results to a group?
Use DBMS_JOB for scheduling a cron job and DBMS_MAIL to send the results through email.
FAQ - Database Testing ( 41 to 50 )
41. What command is used to get back the privileges offered by the GRANT command?
REVOKE
42. What are the privileges that can be granted on a table by a user to others?
INSERT, UPDATE, DELETE, SELECT, REFERENCES, INDEX, EXECUTE, ALTER, ALL
43. Which is the subset of the SQL commands used to manipulate Oracle database structures?
Data Definition Language (DDL)
44. What is Materialized View?
A materialized view is a database object that contains the results of a query. They are local copies of data located remotely or used to create summary tables based on aggregation of a tables data. Materialized views, which store data based on the remote tables are also, know as snapshots.
45. How to write a SQL statement to find the first occurrence of a Non-Zero value?
There is a slight chance the column "a" has a value of 0 which is not null. In that case, you'll loose the information. There is another way of searching the first not null value of a column:SELECT COLUMN_NAME FROM TABLE_NAME WHERE COLUMN_NAME IS NOT NULL AND ROWNUM<2;>
46. Is there any query which is use to find the case sensitivity in each records in database through visual basic?
For case sensitive string comparison in SQL one has to use substring() and ascii() functions in the following way.Get first character of both strings using substring function as substring(str1, 1, 1)Find ascii value of both characters and compare.Put statements 1 and 2 in loop to advance to next characterFor example if (ascii(substring(str1, @pos, 1)) = ascii(substring(str2, @pos, 1)) then @pos = @pos + 1.
47. Which system table contains information on constraints on all the tables created?
USER_CONSTRAINTS
48. What operator tests column for the absence of data?
IS NULL operator.
49. If DELETE ANY TABLE in back-end then what are the triggers will fire automatically (Those triggers are back-end triggers only)?
Oracle has Schema triggers (CREATE OR REPLACE TRIGGER ... ON SCHEMA ... that will
file on DDL commands. You can do things like CREATE OR REPLACE TRIGGER SAVE_OUR_DBBEFORE DROP OR TRUNCATE ON SCHEMAto stop/log attempts to drop a table.
50. How to write a SQL statement to query the result set and display row as columns and columns as row?
TRANSFORM COUNT(ROLL_NO) AS COUNTOFROLL_NO SELECT ACADEMIC_STATUSFROM TBL_ENR_STATUS GROUP BY ACADEMIC_STATUS PIVOT CURNT_STATUS;
REVOKE
42. What are the privileges that can be granted on a table by a user to others?
INSERT, UPDATE, DELETE, SELECT, REFERENCES, INDEX, EXECUTE, ALTER, ALL
43. Which is the subset of the SQL commands used to manipulate Oracle database structures?
Data Definition Language (DDL)
44. What is Materialized View?
A materialized view is a database object that contains the results of a query. They are local copies of data located remotely or used to create summary tables based on aggregation of a tables data. Materialized views, which store data based on the remote tables are also, know as snapshots.
45. How to write a SQL statement to find the first occurrence of a Non-Zero value?
There is a slight chance the column "a" has a value of 0 which is not null. In that case, you'll loose the information. There is another way of searching the first not null value of a column:SELECT COLUMN_NAME FROM TABLE_NAME WHERE COLUMN_NAME IS NOT NULL AND ROWNUM<2;>
46. Is there any query which is use to find the case sensitivity in each records in database through visual basic?
For case sensitive string comparison in SQL one has to use substring() and ascii() functions in the following way.Get first character of both strings using substring function as substring(str1, 1, 1)Find ascii value of both characters and compare.Put statements 1 and 2 in loop to advance to next characterFor example if (ascii(substring(str1, @pos, 1)) = ascii(substring(str2, @pos, 1)) then @pos = @pos + 1.
47. Which system table contains information on constraints on all the tables created?
USER_CONSTRAINTS
48. What operator tests column for the absence of data?
IS NULL operator.
49. If DELETE ANY TABLE in back-end then what are the triggers will fire automatically (Those triggers are back-end triggers only)?
Oracle has Schema triggers (CREATE OR REPLACE TRIGGER ... ON SCHEMA ... that will
file on DDL commands. You can do things like CREATE OR REPLACE TRIGGER SAVE_OUR_DBBEFORE DROP OR TRUNCATE ON SCHEMAto stop/log attempts to drop a table.
50. How to write a SQL statement to query the result set and display row as columns and columns as row?
TRANSFORM COUNT(ROLL_NO) AS COUNTOFROLL_NO SELECT ACADEMIC_STATUSFROM TBL_ENR_STATUS GROUP BY ACADEMIC_STATUS PIVOT CURNT_STATUS;
FAQ - Database Testing ( 31 to 40 )
31. What operator performs pattern matching?
LIKE operator
32. What are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.
33. What is the value of Comm & Sal after executing the following query if the initial value of 'Sal' is 10000?
UPDATE EMP SET SAL = SAL + 1000, COMM = SAL * 0.1;
Sal = 11000, Comm = 1000
34. What is the advantage to use trigger in your PL?
Triggers are fired implicitly on the tables/views on which they are created. There are various advantages of using a trigger. Some of them are:- Suppose we need to validate a DML statement (insert/Update/Delete) that modifies a table then we can write a trigger on the table that gets fired implicitly whenever DML statement is executed on that table.- Another reason of using triggers can be for automatic updating of one or more tables whenever a DML/DDL statement is executed for the table on which the trigger is created.- Triggers can be used to enforce constraints. For eg : Any insert/update/ Delete statements should not be allowed on a particular table after office hours. For enforcing this constraint Triggers should be used.
- Triggers can be used to publish information about database events to subscribers. Database event can be a system event like Database startup or shutdown or it can be a user even like User login in or user logoff.
35. Which command displays the SQL command in the SQL buffer, and then executes it?
You set the LIST or L command to get the recent one from SQL Buffer
36. What the difference between UNION and UNION ALL?
Union will remove the duplicate rows from the result set while Union all does not.
37. How to store directory structure in a database?
We can do it by the following command,
CREATE OR REPLACE DIRECTORY AS 'C:\TMP'
38. How to copy SQL table?
COPY FROM DATABASE TO DATABASE ACTION - DESTINATION_TABLE (COLUMN_NAME, COLUMN_NAME...) USING QUERY Example:COPY FROM SCOTT/TIGER@ORCL92 - TO SCOTT/TIGER@ORCL92- CREATE NEW_EMP – USING SELECT * FROM EMP;
39. Which command executes the contents of a specified file?
START or @
40. What are the different types of Normalization forms?
There are five normal forms. It is necessary for any database to be in the third normal form to maintain referential integrity and non-redundancy.
First Normal Form
Every field of a table (row, column) must contain an atomic value.
Second Normal Form
All columns of a table must depend entirely on the primary key column.
Third Normal Form
All columns of a table must depend on all columns of a composite primary key.
Fourth Normal Form
A table must not contain two or more independent multi-valued facts. This normal form is often avoided for maintenance reasons.
Fifth Normal Form
It is about symmetric dependencies.Each normal form assumes that the table is already in the earlier normal form.
LIKE operator
32. What are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.
33. What is the value of Comm & Sal after executing the following query if the initial value of 'Sal' is 10000?
UPDATE EMP SET SAL = SAL + 1000, COMM = SAL * 0.1;
Sal = 11000, Comm = 1000
34. What is the advantage to use trigger in your PL?
Triggers are fired implicitly on the tables/views on which they are created. There are various advantages of using a trigger. Some of them are:- Suppose we need to validate a DML statement (insert/Update/Delete) that modifies a table then we can write a trigger on the table that gets fired implicitly whenever DML statement is executed on that table.- Another reason of using triggers can be for automatic updating of one or more tables whenever a DML/DDL statement is executed for the table on which the trigger is created.- Triggers can be used to enforce constraints. For eg : Any insert/update/ Delete statements should not be allowed on a particular table after office hours. For enforcing this constraint Triggers should be used.
- Triggers can be used to publish information about database events to subscribers. Database event can be a system event like Database startup or shutdown or it can be a user even like User login in or user logoff.
35. Which command displays the SQL command in the SQL buffer, and then executes it?
You set the LIST or L command to get the recent one from SQL Buffer
36. What the difference between UNION and UNION ALL?
Union will remove the duplicate rows from the result set while Union all does not.
37. How to store directory structure in a database?
We can do it by the following command,
CREATE OR REPLACE DIRECTORY AS 'C:\TMP'
38. How to copy SQL table?
COPY FROM DATABASE TO DATABASE ACTION - DESTINATION_TABLE (COLUMN_NAME, COLUMN_NAME...) USING QUERY Example:COPY FROM SCOTT/TIGER@ORCL92 - TO SCOTT/TIGER@ORCL92- CREATE NEW_EMP – USING SELECT * FROM EMP;
39. Which command executes the contents of a specified file?
START
40. What are the different types of Normalization forms?
There are five normal forms. It is necessary for any database to be in the third normal form to maintain referential integrity and non-redundancy.
First Normal Form
Every field of a table (row, column) must contain an atomic value.
Second Normal Form
All columns of a table must depend entirely on the primary key column.
Third Normal Form
All columns of a table must depend on all columns of a composite primary key.
Fourth Normal Form
A table must not contain two or more independent multi-valued facts. This normal form is often avoided for maintenance reasons.
Fifth Normal Form
It is about symmetric dependencies.Each normal form assumes that the table is already in the earlier normal form.
FAQ - Database Testing ( 21 to 30 )
21. There is Eno and Gender in a table. Eno has primary key and Gender has a check constraints for the values 'M' and 'F'. While inserting the data into the table, M was misspelled as F and F as M. What is the update statement to replace F with M and M with F?
UPDATE
22. What is the use of the DROP option in the ALTER TABLE command?
It is used to drop constraints specified on the table.
23. What is the difference between TRUNCATE and DELETE command?
Both will result in deleting all the rows in the table. TRUNCATE call cannot be rolled back as it is a DDL command and all memory space for that table is released back to the server TRUNCATE is much faster. Whereas DELETE call is an DML command and can be rolled back.
24. Consider the below statements,
TRUNCATE TABLE EMP;
DELETE FROM EMP;
Will the outputs of the above two commands differ?
Both will result in deleting all the rows in the table EMP.
25. What is the advantage of specifying WITH GRANT OPTION in the GRANT command?
The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user.
26. Which date function is used to find the difference between two dates?
MONTHS_BETWEEN
27. Why you need indexing? Where that is stored and what you mean by schema object? For what purpose we are using view?
We can’t create an Index on Index. Index is stored in user_index table. Every object that has been created on Schema is Schema Object like Table, View etc. If we want to share the particular data to various users we have to use the virtual table for the Base table. So that is a view. Indexing is used for faster search or to retrieve data faster from various table. Schema containing set of tables, basically schema means logical separation of the database. View is crated for faster retrieval of data. It's customized virtual table. we can create a single view of multiple tables. Only the drawback is, view needs to be getting refreshed for retrieving updated data.
28. How to find second maximum value from table?
SELECT MAX (FIELD1) FROM TNAME1 WHERE FIELD1=(SELECT MAX (FIELD1) FROM TNAME1 WHERE FIELD1<(SELECT MAX (FIELD1) FROM TNAME1);Field1- Salary fieldTname= Table name.
29. How can we backup the SQL files?
You can backup the SQL files through backup utilities or some backup command in SQL. SAP is ERP software for the organization to integrate the software.
30. How to find out the 10th highest salary in SQL query?
Table - Tbl_Test_Salary Column - int_salarySELECT MAX (INT_SALARY) FROM TBL_TEST_SALARY WHERE INT_SALARY IN(SELECT TOP 10 INT_SALARY FROM TBL_TEST_SALARY ORDER BY INT_SALARY)
FAQ - Database Testing ( 11 to 20 )
11. Which system table contains information on privileges granted and privileges
obtained?
USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD
12. Which system table contains information on constraints on all the tables created?
USER_CONSTRAINTS
13. What is the output of the following query SELECT TRUNC(1234.5678, -2) FROM DUAL;
1200
14. What is the use of DESC in SQL?
DESC has two purposes. It is used to describe a schema as well as to retrieve rows from table in descending order.
Explanation:
The query SELECT * FROM EMP ORDER BY ENAME DESC will display the output
sorted on ENAME in descending order.
15. State True or False: EXISTS, SOME, ANY are operators in SQL?
True
16. There are two tables, Employee and Department. There are few records in employee table, for which, the department is not assigned. The output of the query should contain all the employees’ names and their corresponding departments, if the department is assigned otherwise employee names and null value in the place department name. What is the query?
What you want to use here is called a left outer join with Employee table on the left side. A left outer join as the name says picks up all the records from the left table and based on the joint column picks the matching records from the right table and in case there are no matching records in the right table, it shows null for the selected columns of the right table. eg in this query which uses the key-word LEFT OUTER JOIN. Syntax though varies across databases. In DB2/UDB it uses the key word LEFT OUTER JOIN, in case of Oracle the connector is Employee_table.Dept_id *= Dept_table.Dept_idSQL Server/Sybase : Employee_table.Dept_id(+) = Dept_table.Dept_id
17. What command is used to create a table by copying the structure of another table?
CREATE TABLE.. AS SELECT command
Explanation:
To copy only the structure, the WHERE clause of the SELECT command should contain a false statement as in the following.
CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2;
If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table.
18. State True or False: !=, <>, ^= all denotes the same operation?
True
19. Which function is used to find the largest integer less than or equal to a specific value?
FLOOR
20. What does the following query do?
SELECT SAL + NVL (COMM, 0) FROM EMP;
This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.
obtained?
USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD
12. Which system table contains information on constraints on all the tables created?
USER_CONSTRAINTS
13. What is the output of the following query SELECT TRUNC(1234.5678, -2) FROM DUAL;
1200
14. What is the use of DESC in SQL?
DESC has two purposes. It is used to describe a schema as well as to retrieve rows from table in descending order.
Explanation:
The query SELECT * FROM EMP ORDER BY ENAME DESC will display the output
sorted on ENAME in descending order.
15. State True or False: EXISTS, SOME, ANY are operators in SQL?
True
16. There are two tables, Employee and Department. There are few records in employee table, for which, the department is not assigned. The output of the query should contain all the employees’ names and their corresponding departments, if the department is assigned otherwise employee names and null value in the place department name. What is the query?
What you want to use here is called a left outer join with Employee table on the left side. A left outer join as the name says picks up all the records from the left table and based on the joint column picks the matching records from the right table and in case there are no matching records in the right table, it shows null for the selected columns of the right table. eg in this query which uses the key-word LEFT OUTER JOIN. Syntax though varies across databases. In DB2/UDB it uses the key word LEFT OUTER JOIN, in case of Oracle the connector is Employee_table.Dept_id *= Dept_table.Dept_idSQL Server/Sybase : Employee_table.Dept_id(+) = Dept_table.Dept_id
17. What command is used to create a table by copying the structure of another table?
CREATE TABLE.. AS SELECT command
Explanation:
To copy only the structure, the WHERE clause of the SELECT command should contain a false statement as in the following.
CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2;
If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table.
18. State True or False: !=, <>, ^= all denotes the same operation?
True
19. Which function is used to find the largest integer less than or equal to a specific value?
FLOOR
20. What does the following query do?
SELECT SAL + NVL (COMM, 0) FROM EMP;
This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.
FAQ - Database Testing ( 01 to 10 )
1. What is the use of CASCADE CONSTRAINTS?
When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.
2. What are the different categories of SQL statements?
DDL, DML, DCL, Session Control, System Control.
3. What are the wildcards used for pattern matching?
Underscore (_) for single character substitution & % for multi-character substitution.
4. Why does the following command give a compilation error?
DROP TABLE &TABLE_NAME;
Variable names should start with an alphabet. Here the table name starts with ‘&' symbol. Any table name must start with alphabet. Table names starting with special characters are considered to be invalid hence give error.
5. How can I hide a particular table name of our schema?
You can hide the table name by creating synonyms.(e.g.) You can create a synonym y for table xcreate synonym y for x;
6. What is the parameter substitution symbol used with INSERT INTO command?
&
7. What will be the output of the following query?
SELECT REPLACE (TRANSLATE (LTRIM (RTRIM ('!!ATHEN!!','!'),'!'),'AN','**'),'*','TROUBLE') FROM DUAL;
Ans: TROUBLETHETROUBLE.
8. Difference between VARCHAR and VARCHAR2?
Varchar means fixed length character data (size) i.e., min size-1 and max-2000.
Varchar2 means variable length character data i.e., min-1 to max-4000.
Varchar assigns total length to data. Suppose we have name [20], now with the case of if we entered NARINDER, totally 20 cells will be occupied. But in case of varchar2, 8 cells of memory coz there are 8 elements in that data.
9. What is the difference between DBMS and RDBMS?
1. RDBMS = DBMS + Referential Integrity2. An RDBMS is one that follows 12 rules of CODD.
10. When we give SELECT * FROM EMP; How does oracle respond?
When u give SELECT * FROM EMP; the server check all the data in the EMP file and it displays the data of the EMP file. When we give select * from emp it will shows the records of table emp if the table contain records. If it hasn't any records then it will shows no rows selected.
When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.
2. What are the different categories of SQL statements?
DDL, DML, DCL, Session Control, System Control.
3. What are the wildcards used for pattern matching?
Underscore (_) for single character substitution & % for multi-character substitution.
4. Why does the following command give a compilation error?
DROP TABLE &TABLE_NAME;
Variable names should start with an alphabet. Here the table name starts with ‘&' symbol. Any table name must start with alphabet. Table names starting with special characters are considered to be invalid hence give error.
5. How can I hide a particular table name of our schema?
You can hide the table name by creating synonyms.(e.g.) You can create a synonym y for table xcreate synonym y for x;
6. What is the parameter substitution symbol used with INSERT INTO command?
&
7. What will be the output of the following query?
SELECT REPLACE (TRANSLATE (LTRIM (RTRIM ('!!ATHEN!!','!'),'!'),'AN','**'),'*','TROUBLE') FROM DUAL;
Ans: TROUBLETHETROUBLE.
8. Difference between VARCHAR and VARCHAR2?
Varchar means fixed length character data (size) i.e., min size-1 and max-2000.
Varchar2 means variable length character data i.e., min-1 to max-4000.
Varchar assigns total length to data. Suppose we have name [20], now with the case of if we entered NARINDER, totally 20 cells will be occupied. But in case of varchar2, 8 cells of memory coz there are 8 elements in that data.
9. What is the difference between DBMS and RDBMS?
1. RDBMS = DBMS + Referential Integrity2. An RDBMS is one that follows 12 rules of CODD.
10. When we give SELECT * FROM EMP; How does oracle respond?
When u give SELECT * FROM EMP; the server check all the data in the EMP file and it displays the data of the EMP file. When we give select * from emp it will shows the records of table emp if the table contain records. If it hasn't any records then it will shows no rows selected.
Friday, March 28, 2008
Introduction to Database Testing
What is a Database?
A database is a collection of data that is organized so that its contents can easily be accessed, managed and updated.
A database is a collection of data that is organized so that its contents can easily be accessed, managed and updated.
Basic Unix / Linux Commands
You can find basic unix commands in the below link.
http://www.er.uqam.ca/nobel/r10735/unixcomm.html
http://www.computerhope.com/unix.htm
http://www.ee.surrey.ac.uk/Teaching/Unix/index.html
http://www.ss64.com/bash
http://www.unixguide.net/linux/linuxshortcuts.shtml
These are the wonderful site for unix / Linux. Browse through it. Its really great and interesting
Thursday, March 20, 2008
FAQ - Automation - QTP (191 to 201)
191. Where to use function or action?
Well answer depends on the scenario. If you want to use the OR feature then you have to go for Action only. If the functionality is not about any automation script i.e. a function like getting a string between to specific characters, now this is something not specific to QTP and can be done on pure VB Script, so this should be done in a function and not an action. Code specific to QTP can also be put into a function using DP. Decision of using function/action depends on what any one would be comfortable using in a given situation.
192. How can I check if a checkpoint passes or not?
code:
chk_PassFail = Browser(…).Page(…).WebEdit(…).Check (Checkpoint(”Check1″))
if chk_PassFail then
MsgBox “Check Point passed”
else
MsgBox “Check Point failed”
end if
193. My test fails due to checkpoint failing, Can I validate a checkpoint without my test failing due to checkpoint failure?
code:
Reporter.Filter = rfDisableAll ‘Disables all the reporting stuff
chk_PassFail = Browser(…).Page(…).WebEdit(…).Check (Checkpoint(”Check1″))
Reporter.Filter = rfEnableAll ‘Enable all the reporting stuff
if chk_PassFail then
MsgBox “Check Point passed”
else
MsgBox “Check Point failed”
end if
194. How can I import environment from a file on disk?
Environment.LoadFromFile “C:\Env.xml”
195. How can I check if an environment variable exists or not?
When we use Environment(”Param1″).value then QTP expects the environment variable to be already defined. But when we use Environment.value(”Param1″) then QTP will create a new internal environment variable if it does not exists already. So to be sure that variable exist in the environment try using Environment(”Param1″).value.
196. How to connect to a database?
code:
Const adOpenStatic = 3
Const adLockOptimistic = 3
Const adUseClient = 3
Set objConnection = CreateObject(”ADODB.Connection”)
Set objRecordset = CreateObject(”ADODB.Recordset”)
objConnection.Open “DRIVER={Microsoft ODBC for Oracle};UID=;PWD=“
objRecordset.CursorLocation = adUseClient
objRecordset.CursorType = adopenstatic
objRecordset.LockType = adlockoptimistic
ObjRecordset.Source=”select field1,field2 from testTable”
ObjRecordset.ActiveConnection=ObjConnection ObjRecordset.Open ‘This will execute your Query
If ObjRecordset.recordcount>0 then
Field1 = ObjRecordset(”Field1″).Value
Field2 = ObjRecordset(”Field2″).Value
End if
197. How to compare two Excel Sheets cell by cell?
This code will open two excel sheet and compare each sheet cell by cell, if any changes there in cells , it will highlight the cells in red color in the first sheet.
Set objExcel = CreateObject(”Excel.Application”)
objExcel.Visible = True
Set objWorkbook1= objExcel.Workbooks.Open(”C:\Documents andSettings\zakir\Desktop\zak1.xls”)
Set objWorkbook2= objExcel.Workbooks.Open(”C:\Documents andSettings\zakir\Desktop\zak2.xls”)
Set objWorksheet1= objWorkbook1.Worksheets(1)
Set objWorksheet2= objWorkbook2.Worksheets(1)
For Each cell In objWorksheet1.UsedRange
If cell.Value <> objWorksheet2.Range(cell.Address).Value Then
cell.Interior.ColorIndex = 3′Highlights in red color if any changes in cells
Else
cell.Interior.ColorIndex = 0
End If
Next
set objExcel=nothing
198. How to use sorting in Excel(Ascending and Descending)
Excel Sorting By Row:
Const xlAscending = 1
Const xlNo = 2
Const xlSortRows = 2
Set objExcel = CreateObject(”Excel.Application”)
objExcel.Visible = True
Set objWorkbook = objExcel.Workbooks.Open(”C:\Documents and Settings\zakir\Desktop\zak1.xls”)
Set objWorksheet = objWorkbook.Worksheets(1)
objWorksheet.Cells(1,1).activate
Set objRange = objExcel.ActiveCell.EntireRow
objRange.Sort objRange, xlAscending, , , , , , xlNo, , , xlSortRows
set objExcel=nothing
Excel Sorting By Column :
Const xlAscending = 1′represents the sorting type 1 for Ascending 2 for Desc
Const xlYes = 1
Set objExcel = CreateObject(”Excel.Application”)’Create the excel object
objExcel.Visible = True’Make excel visible
Set objWorkbook = _
objExcel.Workbooks.Open(”C:\Documents and Settings\zakir\Desktop\zak1.xls”)’ Open the document
Set objWorksheet = objWorkbook.Worksheets(1)’select the sheet based on the index .. 1,2 ,3 …
Set objRange = objWorksheet.UsedRange’which select the range of the cells has some data other than blank
Set objRange2 = objExcel.Range(”A1″)’ select the column to sort
objRange.Sort objRange2, xlAscending, , , , , , xlYes
set objExcel=nothing
199. Uninstall a software using VBscript in QTP
This works for uninstalling most applications. In this example I will show how AutoCAD 2005 can be uninstalled using a VBScript.
Open Regedit and look in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall search for the application and find a the product code that is in GUID format looking like this: {5783F2D7-0301-0409-0002-0060B0CE6BBA} It might be something else for you. The code below will uninstall AutoCAD 2005 as well as Express Tools.
Copy the code below into Notepad and give the file the extension vbs.
on error resume nextSet WshShell = CreateObject(”WScript.Shell”)‘ Uninstall Express ToolsWshShell.Run “msiexec /x {5783F2D7-0311-0409-0000-0060B0CE6BBA} /q”,1,true‘ Uninstall AutoCAD 2005WshShell.Run “msiexec /x {5783F2D7-0301-0409-0002-0060B0CE6BBA} /q”,1,true
200. How to create window application using VBscript?
using HTML Application (HTA)
An HTML Application (HTA) is a Microsoft Windows application written with HTML and Dynamic HTML. The ability to write HTAs was introduced with Microsoft Internet Explorer 5.0.
HTAs can be made from regular HTML files by simply changing the file extension to .hta. A regular HTML file is confined to the security model of the web browser - i.e. to communicating with the server, manipulating the page’s object model (usually to validate forms and / or create interesting visual effects) and reading / writing cookies. An HTA runs as a fully trusted application and therefore has more privileges than a normal HTML file - for example an HTA can create / edit / remove files and registry entries.
Because an HTA has more privileges than an HTML page, it cannot be executed via http. Rather, the HTA must be downloaded (just like an EXE file) and executed from local file system.
201. What is a Dictionary Object
Dictionary Object stores data key, item pairs. A Dictionary object stores the items in the array. Each item is associated with a unique key. The key is used to retrieve an individual item and is usually an integer or a string, but can be anything except an array.
Advantages of using it in QTP:
1. can be used as Global variable declaration. so that any test can access the values from it in the run time.
2. You can store and retrieve any number of run time values in to dictionary.
3. It is one of the Parameterization techniques we can use in QTP
Disadvantages:
We can not specify the values in the design time like Datatable , Action parameters, environment variable.
So it is useful only in Runtime , not design time
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