Re: Optimization of repeated expressions

[Konstantin Osipov]

* Baron Schwartz <baron@stripped> [09/01/14 04:41]:

> A friend asked me this question, and I thought I should ask it here
> before I try to figure it out on my own:
> 
>     select id, pow(sum(x),4) +  pow(sum(x),3) +
>         pow(sum(x),2) + sum(x) as z
>     from foo
>     group by id
> 
> Would mysql have to compute sum(x) four times, or is it smart enough to
> do it once then use the result four times?

The sum will be computed 4 times.

You should use an alias instead.

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