Re: Introducing floating point cast into filter drastically changes row estimate

On Wed, Oct 24, 2012 at 3:51 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Wed, Oct 24, 2012 at 3:33 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
>>> Yeah -- I have a case where a large number of joins are happening that
>>> have a lot of filtering based on expressions and things like that.
>>
>> Might be worth your while to install some indexes on those expressions,
>> if only to trigger collection of stats about them.
>
> Not practical -- these expressions are all about 'outlier culling'.
> It's just wasteful to materialize indexes for stastical purposes only.
> Anyways, in this case, I just refactored the query into a CTE.
>
> Hm -- what if you could flag a table dependent expression for being
> interesting for statistics? Or what about planner hints for boolean
> expressions (ducks) ... 'likely(boolexpr)'?

By the way, just in case it wasn't obvious, that was a very much
tongue-in-cheek suggestion. I was just hoping that the final
disposition of this problem isn't: 'there are some queries that are
impossible to plan correctly'. Anyways, thanks for the help.

merlin