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Wildcard % % Performance

  • November 7, 2020 at 6:45 pm

    #3805523

    Hi

    I have a legacy application that uses a like %searchvalue% condition.

    I have looked at using a computed column with reverse(column_like_is_used_on) which also has an index on the computed column.

    The sql is then “select column from table where reverse_column like reverse(‘%searchstring’)

    Which means the like is now “where reverse_column like ‘gnirtshcraes%’

    This will use an index seek but the problem is for it to work I need to use substring or a left to get the rest of the start of the string for it to work and I get an index scan.

    Really I want to get a fully qualified vale from the legacy app to use in the sql but it’s difficult to change it so any advice is appreciated thanks

  • November 8, 2020 at 7:10 pm

    #3805732

    Thanks for posting your issue and hopefully someone will answer soon.

    This is an automated bump to increase visibility of your question.

  • November 8, 2020 at 10:39 pm

    #3805756

    alic wrote:

    This will use an index seek but the problem is for it to work I need to use substring or a left to get the rest of the start of the string for it to work and I get an index scan.

    I guess I'm not understanding why you think you'd need to do that.  Please post the code you're actually using.  A table definition would help, as well.

    --Jeff Moden

    RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
    First step towards the paradigm shift of writing Set Based code:
    ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

    Change is inevitable... Change for the better is not.

    Helpful Links:
    How to post code problems
    How to Post Performance Problems
    Create a Tally Function (fnTally)

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