how to use Case or IF in a where clause?

  • I have a query that joins a base table to a sentTable that tracks records sent from the base table.

    When a record is sent to the user the id is written to the sentTable so that when the user call my proc only the non sent record will then be sent. I am using a left join from my base table to the sentTable (base_rowid = sent_rowid) and my where clause is sent_rowid is null.

    This is if the user send no parameters. However, if the users send say a vendor parameter I want all records for that vendor that have been sent or not.

    so my current where clause is where sent_rowid is null how do I query if the vendor parameter is not null or blank and then ignore the where sent_rowID is null and bring back any record for the vendor.

     

     

  • WHERE sent_rowid is null or vendor = @vendor_param

    ?

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  • An IF...ELSE is a Control-of-Flow element.  It cannot be used inside of atomic statements, because that would make them non-atomic.  I believe that WHERE clauses can only appear in atomic statements, so IF...ELSE elements CANNOT appear in WHERE clauses.

    A CASE expression returns a single value.  It can be used anywhere that an expression can be used.  A common mistake is to try to return a Boolean expression.  T-SQL does not have a Boolean data type, so a CASE expression CANNOT return a Boolean expression.  A workaround is to return a bit or Y/N and then check whether the returned value is "TRUE"/"FALSE".

    Drew

    J. Drew Allen
    Business Intelligence Analyst
    Philadelphia, PA

  • I think this will match what you need, if I understand correctly:

    SELECT ...

    FROM dbo.baseTable bt

    LEFT OUTER JOIN dbo.sentTable st ON st.sent_rowid = bt.rowid

    WHERE ((@vendor IS NULL AND st.sent_rowid IS NULL) OR

    (@vendor IS NOT NULL AND st.vendor LIKE @vendor)

    SQL DBA,SQL Server MVP(07, 08, 09) "It's a dog-eat-dog world, and I'm wearing Milk-Bone underwear." "Norm", on "Cheers". Also from "Cheers", from "Carla": "You need to know 3 things about Tortelli men: Tortelli men draw women like flies; Tortelli men treat women like flies; Tortelli men's brains are in their flies".

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