Re: Optimizing query?

Le jeudi 31 janvier 2013 à 09:49 +0100, Pavel Stehule a écrit :

> any join where result is related to some function result can be very
> slow, because estimation will be out and any repeated function
> evaluation is just expensive.
>

Hi Pavel,

Thank you for the correction. Since we're at it, I have a question
regarding functions in a query :

Suppose I have a query of the form

SELECT my_function(column_1), column_2
FROM my_table
GROUP BY my_function(column_1)
ORDER BY my_function(column_1);

where my_function is a user defined function.

How many times is the function computed?




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