Oracle
Interview Questions and Answers : SQL
------------------------------------------------------------------------------------------
1.
To see current user name
Sql>
show user;
2.
Change SQL prompt name
SQL>
set sqlprompt “Manimara > “
Manimara
>
Manimara
>
3.
Switch to DOS prompt
SQL>
host
4.
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
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.
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