Home Forums Article Discussions Article Discussions by Author Discuss content posted by Simon Liew How efficient is your covered index? RE: How efficient is your covered index?

  • October 9, 2015 at 6:05 pm

    #1832678

    Andre Ranieri (10/9/2015)

    Can I get clarification on SARGability related to the predicate CarrierTrackingNumber = ISNULL(@Carrier, CarrierTrackingNumber)? I would have thought that this predicate is still SARGable since the ISNULL function is performed on the @Carrier variable, not the CarrierTrackerColumn column itself.

    Wouldn't the query optimizer simply evaluate whether @Carrier is NULL at the outset, then apply a NC seek predicate for the CarrierTrackerNumber against the function result?

    I understand that a applying a function against the column itself renders it non-SARGable and potentially forces a scalar calculation for every row in the table, but I might have been operating under a misconception that applying a function against the parameter would still be considered SARGable.

    Thoughts?

    Andre Ranieri

    My thought is that one test is worth a thousand expert opinions. 😉 Test it! :w00t:

    --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)