SQL

1.      Which is the subset of SQL commands used to manipulate Oracle Database structures, including tables?

Data Definition Language (DDL)

2.      What operator performs pattern matching?

LIKE operator

3.      What operator tests column for the absence of data?

IS NULL operator

4.      Which command executes the contents of a specified file?

             START <filename> or @<filename>

5.      What is the parameter substitution symbol used with INSERT INTO command?

             &

6.      Which command displays the SQL command in the SQL buffer, and then executes it?

             RUN

7.      What are the wildcards used for pattern matching?

             _ for single character substitution and % for multi-character substitution

8.      State true or false. EXISTS, SOME, ANY are operators in SQL.

             True

9.      State true or false. !=, <>, ^= all denote the same operation.

             True

10.  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

11.  What command is used to get back the privileges offered by the GRANT command?

             REVOKE

12.  Which system tables contain information on privileges granted and privileges obtained?

             USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD

13.  Which system table contains information on constraints on all the tables created?

             USER_CONSTRAINTS

14.        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.

15.  What is the difference between TRUNCATE and DELETE commands?

             TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.

16.  What command is used to create a table by copying the structure of another table?

Answer :

             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.

17.  What will be the output of the following query?

SELECT REPLACE(TRANSLATE(LTRIM(RTRIM('!! ATHEN !!','!'), '!'), 'AN', '**'),'*','TROUBLE') FROM DUAL;

             TROUBLETHETROUBLE

18.  What will be the output of the following query?

SELECT  DECODE(TRANSLATE('A','1234567890','1111111111'), '1','YES', 'NO' );

Answer :

             NO

Explanation :

The query checks whether a given string is a numerical digit.

19.  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.

20.  Which date function is used to find the difference between two dates?

             MONTHS_BETWEEN