SELECT list block with CASE?

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SELECT list block with CASE?

SqlServerPass

SSCommitted

Points: 1709
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March 4, 2013 at 5:49 am

#271090

is something like this possible?
SELECT
CASE WHEN (@X = 1)
THEN
COLUMN1,
COLUMN2,
COLUMN3
ELSE
COLUMN4,
COLUMN5,
COLUMN6,
END
FROM TABLE1

Viewing 7 posts - 1 through 6 (of 6 total)

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ChrisM@Work SSC Guru Points: 186127 More actions · Answer 1

No, but you can cheat:

DECLARE @X TINYINT = 0

;WITH SampleTable AS (

SELECT SOMECOLUMNS = 'SOMECOLUMNS', COLUMN1 = 'COLUMN1', COLUMN2 = 'COLUMN2', COLUMN3 = 'COLUMN3',

COLUMN4 = 'COLUMN4', COLUMN5 = 'COLUMN5', COLUMN6 = 'COLUMN6'

)

SELECT SOMECOLUMNS, x.*

FROM SampleTable

CROSS APPLY (

SELECT COLUMN1 = 'COLUMN1', COLUMN2 = 'COLUMN2', COLUMN3 = 'COLUMN3' WHERE @X = 1

UNION ALL

SELECT COLUMN4, COLUMN5, COLUMN6 WHERE @X <> 1

) x

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

Adi Cohn-120898 SSC-Dedicated Points: 33944 More actions · Answer 2

One simple way is to use a if block:

If @x=1

Select column1, column2, column3 from MyTable

Else

Select column4, column5, column6 from MyTable

If you insist of doing just one select statement, then if you don't mind that the columns will have the same name regardless of the @x's value, you can use this code:

select case when @x = 1 THEN column1 else column4 end as col1,

case when @x = 1 THEN column2 else column5 end as col2,

case when @x = 1 THEN column3 else column6 end as col3

from MyTable

Adi

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jshahan SSCarpal Tunnel Points: 4622 More actions · Answer 3

DECLARE @X TINYINT = 0
;WITH SampleTable AS (
SELECT SOMECOLUMNS = 'SOMECOLUMNS', COLUMN1 = 'COLUMN1', COLUMN2 = 'COLUMN2', COLUMN3 = 'COLUMN3',
COLUMN4 = 'COLUMN4', COLUMN5 = 'COLUMN5', COLUMN6 = 'COLUMN6'
)
SELECT SOMECOLUMNS, x.*
FROM SampleTable
CROSS APPLY (
SELECT COLUMN1 = 'COLUMN1', COLUMN2 = 'COLUMN2', COLUMN3 = 'COLUMN3' WHERE @X = 1
UNION ALL
SELECT COLUMN4, COLUMN5, COLUMN6 WHERE @X <> 1
) x

ChrisM@Work, please help educate me. There is something very simple here I don't understand.

How does CROSS APPLY join SampleTable to x?

Dung Dinh SSCrazy Points: 2513 More actions · Answer 4

Maybe, you can use a dynamic query

DECLARE @X bit, @strSQL nvarchar(2000)

SET @X = 1

SET @strSQL =' SELECT ' + CASE WHEN @X = 1 THEN ' COLUMN1,COLUMN2,COLUMN3'

ELSE ' COLUMN4,COLUMN5,COLUMN6' END

+ ' FROM TABLE1 '

EXEC (@strSQL)

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 5

jshahan (3/5/2013)
DECLARE @X TINYINT = 0
;WITH SampleTable AS (
SELECT SOMECOLUMNS = 'SOMECOLUMNS', COLUMN1 = 'COLUMN1', COLUMN2 = 'COLUMN2', COLUMN3 = 'COLUMN3',
COLUMN4 = 'COLUMN4', COLUMN5 = 'COLUMN5', COLUMN6 = 'COLUMN6'
)
SELECT SOMECOLUMNS, x.*
FROM SampleTable
CROSS APPLY (
SELECT COLUMN1 = 'COLUMN1', COLUMN2 = 'COLUMN2', COLUMN3 = 'COLUMN3' WHERE @X = 1
UNION ALL
SELECT COLUMN4, COLUMN5, COLUMN6 WHERE @X <> 1
) x
ChrisM@Work, please help educate me. There is something very simple here I don't understand.
How does CROSS APPLY join SampleTable to x?

The second to last line of my sig is a link to Paul White's famous APPLY articles. Well worth a read. APPLY without a table reference simply means calculate this and affects, and returns results to, the "current row".

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

jshahan SSCarpal Tunnel Points: 4622 More actions · Answer 6

Thanks for the response and the reference. I've got to wrap my brain around this. Been driving me nuts.