Loop through Column Names in a table and do a set of operations - SQL Server 2008

Question

Thank you for helping me out through my previous tides.. I am currently working on SQL Server 2008 for one of my project, a part of which needs to use 22 columns for a set of similar operations.

The column names only differ by the number, e.g.

C1_1,C1_2,c1_3

Is there any way to loop through the column names? I tried out the following code, but it throws out an error

DECLARE @i INT
SET @i=2
while (@i<=22)
begin

    SELECT [DEF].[CONCATENATE], SUM(DEF.[C1_+@i+_PREV]) as   
    [C1_@i_prev]
    INTO #TMP_C1_@i_CONCATENATE_PREV
    FROM DEF    
    GROUP BY DEF.[CONCATENATE]

    SELECT [ABC].[CONCATENATE], SUM(ABC.[C1_@i_CURR]) as 
    [c1_@i_curr]
    INTO #TMP_C1_@i_CONCATENATE_CURR
    FROM ABC
    GROUP BY ABC.[CONCATENATE]

    UPDATE #tmp_var_concatenate_c1_@i
SET [Amount] = #TMP_C1_@i_CONCATENATE_PREV.[C1_@i_PREV]
FROM #tmp_var_concatenate_c1_@i
INNER JOIN 
#TMP_C1_@i_CONCATENATE_PREV ON
#tmp_var_concatenate_c1_@i.[CONCATENATE] = #TMP_C1_@i_CONCATENATE_PREV.
    [CONCATENATE]

Please forgive my ignorance, if I am doing something idiotic.

Thanks

This is part of the code in which the code is burping.

alter table #tmp_var_concatenate_C1_'+cast(@i as varchar)+'
                    add [ColA] varchar(255),
                    [ColB] Varchar(255),
                    [ColC] Varchar(255),
                    [ColD] VARCHAR(50),
                    [ColE] MONEY,
                    [ColF] MONEY

Is it because of the #tables that I am using ?? but, ideally, it shouldnt be an issue whether am using a Temp table or a reg. one..

Answer 1

You can use dynamic sql:

DECLARE @SQL varchar(max), @i INT
SET @i=2
while (@i<=22)
begin

/* Then cover all calculations with this one: */

SET @SQL='SELECT [DEF].[CONCATENATE], SUM(DEF.[C1_'+cast(@i as varchar)+'_PREV]) as   
    [C1_'+cast(@i as varchar)+'_prev]
    INTO #TMP_C1_'+cast(@i as varchar)+'_CONCATENATE_PREV
    FROM DEF    
    GROUP BY DEF.[CONCATENATE]

/* and all your code with the same trick in @i to the END */

'

--PRINT (@SQL) -- print it before use to see the result script

EXEC (@SQL)

/* Than do your iterations etc. */
set @i+=1

end 

And don't forget to substitute all ' inside @SQL with ''. Also you need to do all manipulations with temp tables inside @SQL, if you want to do final update outside the dynamic sql, just make tables real and then delete them.

[UPDATE] As far as you faced with problem of altering temp tables, I tried to reproduce this error, but nothing happens, everything works fine. Please use this code as an example.

declare @sql varchar(max),@i int
set @i=2
while @i<=22
begin
    set @sql='
        select ID,Code into #TMP_C1_'+cast(@i as varchar)+'_CONCATENATE_PREV from (select 0 as ID, ''a'' as Code) t1
        alter table #TMP_C1_'+cast(@i as varchar)+'_CONCATENATE_PREV add [Col1] varchar(255), [Col2] Varchar(255), [Col3] Money
        select * from #TMP_C1_'+cast(@i as varchar)+'_CONCATENATE_PREV'
    --print (@sql)
    exec (@sql)
    set @i+=1
end

First, I create temp table with dynamic name. Second, add new columns. The last is successful verifying. Did you execute all creations/alters in the same @sql-batch? If no, this won't work, because this tables are available only inside this batch (that's why we used varchar(max) when declared). Please describe your actions in details, maybe there is a mistake somewhere.