Re: [SQL] Good Optimization

>
> Bruce Momjian wrote:
> >=20
> > Added to TODO:
> >=20
> > * In WHERE x=3D3 AND x=3Dy, add y=3D3
>
> I don't know if I'm way off, but wouldn't removing "x=3Dy" improve
> performance further?

Maybe in the simple case above. But it will probably change
the result set if someone issues

SELECT a.x, b.y FROM a, b WHERE a.x >= 10
AND a.x <= 19
AND a.x = b.x;

which should then get rewritten into

SELECT a.x, b.y FROM a, b WHERE a.x >= 10
AND a.x <= 19
AND a.x = b.x
AND b.x >= 10
AND b.x <= 19;

This time the "a.x = b.x" is important!

IMHO we're improving optimization more and more on the cost
of query parse/rewrite/optimize/plan time. Thus performance
of statements that EXECUTE fast slows down more and more.
Isn't it time to think about some (maybe shared)
"parsetree->plan" cache that provides ready to use plans if
only Const values have changed?

Jan

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