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SELECT list block with CASE?


SELECT list block with CASE?

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SQL Mad Rafi
SQL Mad Rafi
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Group: General Forum Members
Points: 123 Visits: 363
is something like this possible?

SELECT

CASE WHEN (@X = 1)
THEN
COLUMN1,
COLUMN2,
COLUMN3
ELSE
COLUMN4,
COLUMN5,
COLUMN6,
END

FROM TABLE1
ChrisM@Work
ChrisM@Work
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Points: 16966 Visits: 19557
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
Exploring Recursive CTEs by Example Dwain Camps
Adi Cohn
Adi Cohn
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Group: General Forum Members
Points: 3785 Visits: 6513
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
jshahan
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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
Dung Dinh
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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
ChrisM@Work
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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
Exploring Recursive CTEs by Example Dwain Camps
jshahan
jshahan
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Group: General Forum Members
Points: 560 Visits: 2086
Thanks for the response and the reference. I've got to wrap my brain around this. Been driving me nuts.
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