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Thread: SubQuery Performance

  1. #1
    Join Date
    Aug 2010

    SubQuery Performance

    Hi All,

    I have a poor performance SQL as following. The table has about 200M records, each employee have average 100 records. The query lasts about 3 hours. All I want is to update the flag for highest version of each client's record. Any suggestion is welcome!



    update empTbl A
    set flag=1
    rec_ver =
    ( select max(rec_ver)
    from empTbl
    where empNo = A.empNo)

    ===Table empTbl=====

    int empNo;
    int flag;
    char[256] empDesc;
    int rec_ver;

  2. #2
    Join Date
    Mar 2007
    Ft. Lauderdale, FL
    Please do tell there is an index on empTbl.empNo

    Post execution plan, please.
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.

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