Basic Oracle interview questions and answers for freshers

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Oracle is also called oracle RDBMS ,produced and marketed by Oracle.The Oracle RDBMS stores data logically in the form of tablespaces and physically in the form of data files.

Here are oracle questions asked in interview :

1. To see current user name

Sql> show user;

2.How do you switch from an init.ora file to a spfile?

Issue the create spfile from pfile command.

3. Switch to DOS prompt

SQL> host

4.What is the difference between a hot backup and a cold backup and the benefits associated with each?

A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode.

Benefits:

The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any ball in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk.

5. How do I display row number with records?

To achive this use rownum pseudocolumn with query, like SQL> SQL> select rownum, ename from emp;

Output:

1 Scott

2 Millor

3 Jiyo

4 Smith

6. Display the records between two range

select rownum, empno, ename from emp where rowid in

(select rowid from emp where rownum <=&upto

minus

select rowid from emp where rownum<&Start);

Enter value for upto: 10

Enter value for Start: 7

ROWNUM EMPNO ENAME

——— ——— ———-

1 7782 CLARK

2 7788 SCOTT

3 7839 KING

4 7844 TURNER

7. I know the nvl function only allows the same data type(ie. number or char or date

Nvl(comm, 0)), if commission is null then the text “Not Applicable” want to display, instead of

blank space. How do I write the query?

SQL> select nvl(to_char(comm.),’NA’) from emp;

Output :

NVL(TO_CHAR(COMM),’NA’)

———————–

NA

300

500

NA

1400

NA

NA

8. Oracle cursor : Implicit & Explicit cursors

Oracle uses work areas called private SQL areas to create SQL statements.

PL/SQL construct to identify each and every work are used, is called as Cursor.

For SQL queries returning a single row, PL/SQL declares all implicit cursors.

For queries that returning more than one row, the cursor needs to be explicitly declared.

9. Explicit Cursor attributes

There are four cursor attributes used in Oracle

cursor_name%Found, cursor_name%NOTFOUND, cursor_name%ROWCOUNT, cursor_name%ISOPEN

10. Implicit Cursor attributes

Same as explicit cursor but prefixed by the word SQL

SQL%Found, SQL%NOTFOUND, SQL%ROWCOUNT, SQL%ISOPEN

Tips : 1. Here SQL%ISOPEN is false, because oracle automatically closed the implicit cursor after

executing SQL statements.

: 2. All are Boolean attributes.

11. Find out nth highest salary from emp table

SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B

WHERE a.sal<=b.sal);

Enter value for n: 2

SAL

———

3700

12. To view installed Oracle version information

SQL> select banner from v$version;

13. Display the number value in Words

SQL> select sal, (to_char(to_date(sal,’j'), ‘jsp’))

from emp;

the output like,

SAL (TO_CHAR(TO_DATE(SAL,’J'),’JSP’))

——— —————————————————–

800 eight hundred

1600 one thousand six hundred

1250 one thousand two hundred fifty

If you want to add some text like,

Rs. Three Thousand only.

SQL> select sal “Salary “,

(‘ Rs. ‘|| (to_char(to_date(sal,’j'), ‘Jsp’))|| ‘ only.’))

“Sal in Words” from emp

/

Salary Sal in Words

——- ——————————————————

800 Rs. Eight Hundred only.

1600 Rs. One Thousand Six Hundred only.

1250 Rs. One Thousand Two Hundred Fifty only.

14. Display Odd/ Even number of records

Odd number of records:

select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);

1

3

5

Even number of records:

select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)

2

4

6

15. Which date function returns number value?

months_between

16. Any three PL/SQL Exceptions?

Too_many_rows, No_Data_Found, Value_Error, Zero_Error, Others

17. What are PL/SQL Cursor Exceptions?

Cursor_Already_Open, Invalid_Cursor

18. Other way to replace query result null value with a text

SQL> Set NULL ‘N/A’

to reset SQL> Set NULL ‘’

19. What are the more common pseudo-columns?

SYSDATE, USER , UID, CURVAL, NEXTVAL, ROWID, ROWNUM

20. What is the output of SIGN function?

1 for positive value,

0 for Zero,

-1 for Negative value.

21. What is the maximum number of triggers, can apply to a single table?

12 triggers.

22. How do I eliminate the duplicate rows ?

SQL> delete from table_name where rowid not in (select max(rowid) from table group by

duplicate_values_field_name);

or

SQL> delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from

table_name tb where ta.dv=tb.dv);

Example.

Table Emp

Empno Ename

101 Scott

102 Jiyo

103 Millor

104 Jiyo

105 Smith

Delete ename from emp a where rowid < ( select min(rowid) from emp b where a.ename = b.ename);

The output like,

Empno Ename

101 Scott

102 Millor

103 Jiyo

104 Smith

24. Change SQL prompt name

SQL> set sqlprompt “Manimara > “

Manimara >

Manimara >

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