case in where clasue

I am trying to write a query where I think I can use CASe statement . So what I want to do is say if the value is 0 look in one table other wise look in another table.

Some thing like this

CASE WHEN PROMOTYPE = 0
                   THEN
                        PT.newCode = 'XXX'
                   ELSE
                        PC.codeNAme = 'XCXX'
                   END
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erikTsomikSystem Architect, CF programmer Asked:
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PortletPaulConnect With a Mentor Commented:
If this logic you have provided is correct:

CASE WHEN PROMOTYPE = 0
                   THEN
                        PT.newCode = 'XXX'
                   ELSE
                        PC.codeNAme = 'XCXX'
                   END

Then the conventional where conditions provided by Scott will match that logic:

WHERE (
         (PROMOTYPE = 0 AND PT.newCode = 'XXX')
      OR
         (PROMOTYPE <> 0 AND PC.codeNAme = 'XCXX')
      )

I cannot see any point to using a  case expression in the where clause for such a simple need.

+edit,
unless you have an expectation about NULLs in PROMOTYPE that isn't met by this logic.

It would be useful to provide data instead of just saying it doesn't work.
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Scott PletcherSenior DBACommented:
WHERE
    ( (PROMOTYPE = 0 AND PT.newCode = 'XXX') OR
      (PROMOTYPE <> 0 AND PC.codeNAme = 'XCXX') )

Or, to use a CASE:

WHERE 1 =
    CASE WHEN PROMOTYPE = 0 THEN CASE WHEN PT.newCode = 'XXX' THEN 1 ELSE 0 END
    ELSE CASE WHEN PC.codeNAme = 'XCXX' THEN 1 ELSE 0 END
    END
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erikTsomikSystem Architect, CF programmer Author Commented:
Thanks but it did not work, Now I get only with promotype =0 and none for promoType=1
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
Assuming both PT and PC tables are referenced via FROM..JOIN, and PT.newCode and pc.CodeName have the same datatype..
SELECT blah, blah, blah, 
   CASE WHEN PROMOTYPE = 0 THEN PT.newCode 
   ELSE PC.codeNAme END as name_goes_here
FROM whatever

Open in new window

btw if it helps I have an article out there called SQL Server CASE Solutions that is an code-and-image-heavy tutorial on CASE blocks.
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