What is Differnce between Decode and Case?

Decode
1.It’s a function
2.can compare only discrete vaules
3.Pl/Sql standards
4.cannot process null

Case
1.It's an Expression
2.can hande range values
3.ANSI Standards
4.Processing time is faster when compared to Decode
5.can process null


Decode
The default operator for comparison is '=',
for e.g select deptno,decode
(deptno,10,'dept10',20,dept20,default)

so if the deptno=10 then the value is replaced by dept10
and so on,

whereas in Case:

we can use any operator other than '=',
for e.g
select deptno,
case when deptno=10 and sal>1000 then 'dept10'
else
'dept20'




Decode: using for reporting purpose. and it is implemented
by if stmt.
Ex: select decode(job,'CLERK','executive',job) from emp;

Case : implemented by if & elsif condition. it is using
pl/sql equality conditionality.
Ex : select case job='CLERK' then 'executive' else 'no' end
a from emp;

it is also used for multipul colms & multi conditions.

in above stmt a is reffered alias name.




There is one more Important difference between CASE and DECODE

DECODE can be used Only inside SQL statement....
But CASE can be used any where even as a paramtre of a function/procedure

Eg:-


Code: [Select all] [Show/ hide]SQL> create or replace procedure pro_01(n number) is
2 begin
3 dbms_output.put_line(' The number = '||n);
4 End;
5 /

Procedure created.

SQL> set serverout on
SQL> var a varchar2(5);
SQL> Begin
2 :a := 'ONE';
3 End;
4 /

PL/SQL procedure successfully completed.

SQL> Begin
2 pro_01(Decode(:a,'ONE',1,0));
3 End;
4 /
pro_01(Decode(:a,'ONE',1,0));
*
ERROR at line 2:
ORA-06550: line 2, column 9:
PLS-00204: function or pseudo-column 'DECODE' may be used inside a SQL
statement only
ORA-06550: line 2, column 2:
PL/SQL: Statement ignored


SQL> Begin
2 pro_01(case :a when 'ONE' then 1 else 0 end);
3 End;
4 /
The number = 1

PL/SQL procedure successfully completed.