| From: | Joe <dev(at)freedomcircle(dot)net> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, George Pavlov <gpavlov(at)mynewplace(dot)com>, pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: huge disparities in =/IN/BETWEEN performance |
| Date: | 2007-02-09 04:12:14 |
| Message-ID: | 1170994335.697.55.camel@pampa |
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| Lists: | pgsql-sql |
Hi Tom,
On Thu, 2007-02-08 at 22:50 -0500, Tom Lane wrote:
> There's a datatype abstraction issue involved: what does it take to
> prove that "x >= 10 AND x <= 10" is equivalent to "x = 10"? This
> requires a nontrivial amount of knowledge about the operators involved.
> We could probably do it for operators appearing in a btree operator
> class, but as Alvaro says, it'd be cycles wasted for non-dumb queries.
Are you saying the planner is datatype-agnostic and can't tell that x
is, say, as in the example above, an INTEGER and therefore cannot
transform one expression into another? What about "x = 10 AND x < 5"?
Can't it reduce that to FALSE?
Joe
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