Saturday, March 29, 2008

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?

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?



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.

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