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Logical Equivalence and Query Tuning

Erik Darling didn’t warn us that there would be math:

Often when query tuning, I’ll try a change that I think makes sense, only to have it backfire.

It’s not that the query got slower, it’s that the results that came back were wrong different.

Now, this can totally happen because of a bug in previously used logic, but that’s somewhat rare.

And wrong different results make testers nervous. Especially in production.

This is where knowledge of abstract math and logic (like De Morgan’s Laws, both of which I’ve used to tune queries in the past because I’m a nerd) can pay off