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Question on best place to use a function

  • May 5, 2011 at 1:47 pm

    #249919

    Suppose TableA has 100 million rows. Is it better, from a performance standpoint, to write the query like such

    select * from TableA where SomeFunction(col1)=@VariableA

    or

    Select * from TableA where col1 = ReverseOfSomeFunction(@VariableA)

    Or does it make no difference? For Argument's sake, let's say there is a non-clustered index on col1.

    I hope this makes sense

    Thanks

  • May 5, 2011 at 3:03 pm

    #1320710

    better:

    Select * from TableA where col1 = ReverseOfSomeFunction(@VariableA)

    Since the index is on col1, so it would be used and speed things up and would result in an index seek for a single value; maybe in andex scan.

    if you wrap the column in a function, every row will get formatted, then compared, which requires a table scan.

    Lowell

    --help us help you! If you post a question, make sure you include a CREATE TABLE... statement and INSERT INTO... statement into that table to give the volunteers here representative data. with your description of the problem, we can provide a tested, verifiable solution to your question! asking the question the right way gets you a tested answer the fastest way possible!

  • May 6, 2011 at 10:15 pm

    #1321358

    Totally Agreed. To take advantage of index you must use "where col1 = function(@var1)".

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