Select List for a Conditional Group By

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Hi,

Here's a SQL Query I intend to write

SQL

SELECT CASE COUNT(*) WHEN 1 THEN ColA ELSE MAX(ColA) END FROM tblMyTable GROUP BY CASE Cond1 WHEN 1 THEN ColB END

It's a conditional group by. When the group by is not applied, I need the column A's value. And If it's grouped then I want to the Max of Column A's values.

As expected this shows the error

invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Any suggestions?

Posted 16-Sep-11 3:45am

Jyothikarthik_N

Updated 16-Sep-11 3:47am

v2

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sachin10d · Answer 1 · 2011-09-16T03:58:00

Solution 1

I think you will have to use dynamic SQL

SQL

declare @strSql nvarchar(100)
declare @count int
select @count = COUNT(*) from tblMyTable where ID = 1
set @strSql ='select ' +
                case @count when 1 then ' ColA '
                else 'MAX(ColA)' end
+ 'from tblMyTable '
+ 'group by ' + case @count when 1 then  ' ColA '
                else ' ColB ' end

sp_executesql @strSql

Posted 16-Sep-11 3:58am

sachin10d

Updated 16-Sep-11 4:09am

v2

Comments

[no name] 19-Sep-11 1:33am

Hi Sachin,

Thanks for your reply. Can you suggest an alternate solution, as this would return me an incorrect answer.

Right now the execution goes like this.

Q1*+ U Q2*

U - Union
* - Where conditions
+ - Group By

The first query (Q1) is grouped by and returns some values
The next query (Q2) returns by default 1 for all the remaining rows.

And combined, they have values for all rows.

I'm looking at combining both queries into one (Reason: Replicating where conditions with just minor change, Two Selects, One union all adds up to resource wastage)