Concerns
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.
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!
Going Further
If this is the kind of SQL Server stuff you love learning about: these days I have AI do the annoying stuff for me. My new video course teaches you to work the same way, and I teach whole teams in a one-day workshop. Someone still has to know enough SQL Server to keep the robots in check, and that’s what my training is for.