Implicit Conversion Is A SARGability Problem


If you compare the things that non-SARGable queries cause issues with alongside the things that bad implicit conversions cause issues with, it’s an identical list.

  • Increased CPU
  • Inefficient use of indexes
  • Poor cardinality estimation
  • Maybe a bad memory grant based on that
  • Some “row by row” event

Though we often bucket the problems separately, they’re really the same thing.

That’s because, under the covers, something similar happens.

Four letters

If you replace “CONVERT_IMPLICIT” with any other function, like ISNULL, COALESCE, DATEADD, DATEDIFF, etc. you may see the same performance degradation.

Probably not the most thought provoking thing you’ve ever heard, but if you understand why one is bad and not the other, this may help you.

Thanks for reading!

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