In this post we will discuss some basic Oracle Interview questions and answers. Answers given are very precise. Please help me to improve the answer if you think so. I will be regularly updating this post.
1. What is the difference between Procedure and Function ?
Ans:-
a) Function must return a value and procedure need not.
b) Function can be used in SQL with some restrictions. Procedure cannot be called directly from SQL.
2. What is the difference between Anonymous blocks and sub programs ?
Ans :-
a) Anonymous blocks are unnamed blocks which are not stored anywhere while sub programs are compiled and stored in database.
b) Anonymous blocks compile at run time.
3. What is the difference between DELETE and TRUNCATE ?
Ans:-
a) DELETE is a DML command and TRUNCATE is a DDL command.
b) TRUNCATE re-set the memory blocks after execution and much faster than DELETE in most of the circumstances.
4. What is Implicit Cursor and Explicit Cursor ?
a) Implicit Cursor is defined and controlled by Oracle Internally.
Example :-
declare
v_ename varchar2(50);
begin
select ename into v_ename from emp where empno = 10;
end;
select query used in above PL/SQL block is an implicit cursor
b) Explicit Cursor is defined and controlled programatically.
Example :-
declare
v_ename varchar2(50);
Cursor Cur_ename is select ename into v_ename from emp where empno = 10;
begin
Open Cur_ename;
Fetch Cur_ename into v_ename;
Close Cur_ename;
end;
5. Difference between DECODE and CASE
Ans :- Click here
6. How to find Nth highest salary ?
Ans :- Click here
7. Difference between UNION and UNION ALL clause
Ans :- Click here
8. What is Autonomous Transaction ?
Ans :- Click here
9. Difference between REPLACE and TRANSLATE functions
Ans:- Click here
10. What is LEAD and LAG function used for ?
Ans:- Click here
11. Explain function or procedure overloading
Ans:- Click here
12. What is MERGE used for ?
Ans:- Click here
13. What is GREATEST and LEAST function used for ?
Ans:- Click here
14. Where we use SOUNDEX function ?
Ans:- Click here
15. What is COALESCE function ?
Ans:- Click here
16. Difference between TRUNC and ROUND function
Ans:- Click here
17. How to convert Julian Date to date ?
Ans :- Using ‘JSP’ format string
SQL > select to_char(to_date(2456317,’JSP’),’dd-Mon-yyyy’) as day from dual;
DAY
————
24-Jan-2013
18. How to convert date to Julian Date format ?
Ans :- Using ‘J’ format string
SQL > select to_char(to_date(’24-Jan-2013′,’dd-mon-yyyy’),’J’) as julian from dual;
JULIAN
——-
2456317
19. What is the difference between PRIMARY KEY and UNIQUE KEY constraints ?
1. UNIQUE KEY columns can have null values but PRIMARY KEY column cannot accept null values.
2. A table can have only one PRIMARY KEY column but many UNIQUE KEY columns allowed.
( I can spot only two. Any more difference ? )
20. What is PRAGMA ?
PRAGMA is Oracle keyword to telling the compiler to do some special work.
Examples :-
21. What is Constraint ? How many constraints are available ?
Ans :- Explained in another post
22. What is Cartesian Product ?
If two or more tables are joining without join condition will result into Cartesian products.
If table A has 2 rows and table B has 4 rows then Cartesian product between A and B will return 8 rows ( 2 multiply by 4 )
You want to improve the answer ? Please add your comment or send email.
See Also
Install Oracle in Ubuntu 12.04
Latest version of Oracle database – Oracle 12c
Oracle 12C New Features
Notepad++ – Tips and Tricks
Remote desktop in ubuntu 12.04
Install Skype in Ubuntu 12.04
Install Microsoft fonts in Ubuntu 12.04
Latest version of Oracle database – Oracle 12c
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