Re: optimizing abs()

[Toa Sty]

Hi Michiel,

I'm not sure that MySQL does much in the way of function specific optimisations, so it acts like it doesn't know anything the result of abs(). As a result, it just scans the table calculating abs() and comparing the result to your value.

Your workaround is just what I'd do in this case. In most other cases like this you have to add a pre-computed column which is pretty ugly.

Function indexes (eg http://www.postgresql.org/docs/8.1/interactive/indexes-expressional.html) in MySQL would be about the best thing ever. Don't think they're likely to happen soon though. :-/

Toasty

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