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IS NOT NULL vs <> ''

  • March 1, 2012 at 7:35 am

    #265373

    What is the difference between the below queries:

    select * from table where col IS NOT NULL and

    select * from table where col <> ''

    Thanks in advance

  • March 1, 2012 at 7:42 am

    #1453626

    The first finds rows where the column is not NULL

    The second finds rows where the column does not equal an empty string.

    CREATE TABLE Blah (

    SomeString char(2)

    )

    Insert into Blah (null)

    Insert into Blah ('')

    Insert into blah ('abc')

    IS NOT NULL will match 2 rows, != '' will match 1.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

  • March 1, 2012 at 11:03 am

    #1453787

    Thank you very much.

    How the below query works?

    Select * from table

  • March 1, 2012 at 11:35 am

    #1453804

    Errrr, it retrieves all rows from the table.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

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