Calculated column in where-clause - performance
mysql, performance
Solution
You can use HAVING to filter on a computed column:
SELECT a,b,c,(a*b+c) AS d, n FROM table
HAVING d > n
ORDER by d
Note that you need to include `n` in the SELECT clause for this to work.
Problem
Since you can't use a calculated column in a where-clause in MySQL like this: ``` SELECT a,b,c,(a*b+c) AS d FROM table WHERE d > n ORDER by d ``` you have to use ``` SELECT a,b,c,(a*b+c) AS d FROM table WHERE (a*b+c) > n ORDER by d ``` Is the calculation (in that example "(a*b+c)" executed once per row or twice? Is there a way to make it faster? I find it strange it's possible to ORDER on the column but not to have a WHERE-clause.