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NVL,NVL2,DECODE,COALESCE functions in Oracle

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All the functions mentioned in the above title are mainly used in evaluation of data whether it is null or not.
.
Lets see in details how these functions work and what are the differences between them

NVL

Syntax: NVL ( expr1 , expr2 )

 If the expr1 is null then expr2 value is returned, if expr1 value is not null then expr1 value is returned.

 NVL2

 Syntax: NVL2(expr1,expr2,expr3)

 if the expr1 is null then expr3 value is returned, if expr1 value is not null then expr2 value is returned.

COALESCE

 Syntax: COALESCE(expr1,expr2,expr3...)

it returns first non null expression value in the list.

DECODE

 Decode is enhanced version of case statement let me explain you with a sample query

 select
initcap(substr(pub_name,1,20)) publisher_name,
decode(book_type,'computer',1,0) media
from
publisher 
Here decode statement works like if the column book_type has computer value then it is returned as 1 else 0 

 Similar to case statement

 case when book_type='computer'
then 1
else 0
end media

 Hope this article helps you in understanding the above functions.

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