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I was reading a function in Oracle namely “Decode”. It is very handy when it comes to search a variable and return the result based on search. It has been asked on multiple forums, what the EQUIVALENT of DECODE IN SQL SERVER is? Basically, we can achieve the same in SQL Server using Case and IIF statements.

Lets view the decode in Oracle.

Select DECODE(PoleDirection, 'North','N', 'South','S', 'East','E','WEST','W', 'Not Applicable') AS [Poles]
FROM TablePoles

Lets view the Equivalent Code in SQL Server.

Declare @PoleDirection as varchar(10)
Set @PoleDirection= 'North'

SELECT CASE WHEN @PoleDirection = 'North' THEN 'N'
WHEN @PoleDirection = 'South' THEN 'S'
WHEN @PoleDirection = 'East' THEN 'E'
WHEN @PoleDirection = 'WEST' THEN 'W'
ELSE 'Not Applicable' END AS [Poles]

Decode function in SQL server

Given below is the DECODE function in SQL SERVER.

Create FUNCTION [dbo].[DECODE] (
	@Expression nvarchar(max),
	@String nvarchar(Max))
RETURNS nvarchar(Max)
AS
Begin
Declare @Delimiter as varchar(1)
Declare @ReturnValue as nvarchar(max)
Set @Delimiter=','
Declare @Xml AS XML 
 
Declare @Table TABLE(
    [ID] int Identity(1,1),
	Splitcolumn VARCHAR(MAX)
)   
SET @Xml = cast(('<A>'+replace(@String,@Delimiter,'</A><A>')+'</A>') AS XML)    
INSERT INTO @Table SELECT A.value('.', 'varchar(max)') as [Column] FROM @Xml.nodes('A') AS FN(A)   

IF (Select Count (*) from @Table A Where @Expression=A.[SplitColumn])=1
Begin
	Select top 1 @ReturnValue=B.[Splitcolumn] from @Table A
	Left Join @Table B On A.[ID]<B.[ID]
	Where @Expression=A.[SplitColumn]
	Order By A.[ID]
END
Else
BEGIN
	Select top 1 @ReturnValue=A.[Splitcolumn]  from @Table A
	Order By A.[ID] DESC
END
RETURN @ReturnValue
End
GO

Syntax :

    Decode (expression , search , result [, search , result]... [, default])

Examples 1:

Create table tbl_Sample1
(
 [ID] varchar(6),
 [Employee Name] varchar(50),
 [Performance Evaluation] varchar(10)
)
GO
Insert into tbl_Sample1 values ('STD001','Bob','Excellent')  
Insert into tbl_Sample1 values ('STD002','Alexander','Good')  
Insert into tbl_Sample1  values ('STD003','Hosanna','Fair')  

GO
SELECT [ID],[Employee Name],[Performance Evaluation]
,dbo.Decode( [Performance Evaluation],'Excellent,100,Good,80,Fair,60,Unknown') 
as [Performace Index]
from tbl_Sample1
GO

Examples 2:

Create table tbl_Sample2
(
 [ID] int ,
 [Country] varchar(50),
 [Short Name] varchar(3)
)
GO

Insert into tbl_Sample2 Values (1,'PAKISTAN','PAK')
Insert into tbl_Sample2 Values (2,'UNITED STATES OF AMERICA','USA')
Insert into tbl_Sample2 Values (3,'UNITED KINGDOM','UK')
Insert into tbl_Sample2 Values (4,'UNITED ARAB EMIRATES','UAE')
go

SELECT [ID],[Country],[Short Name]
,dbo.Decode([Short Name],'PAK,RS,USA,USD,UK,GBP,UAE,AED,Not Matched') 
as [Currency]
from tbl_Sample2
GO

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