Re: Using functions as filters in queries

Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> writes:
> Of course, I misread what explain did (without trying the
> enable_seqscan=off case) and this is still not indexable because even
> after that, you'll not get a clause on the outside that it considers
> indexable. It is smart enough (7.4 anyway) to make the filter ((t.*).n)=5
> which I thought it'd index, but doesn't. :(

Note that inline-expansion of SQL functions like this is new for 7.4;
it's not done in any current release.

I think the extra step to make this expression indexable is probably not
too hard: the constant-expression folder needs to be taught that
extracting a field from a whole-row Var can be replaced by a Var
reference to the field, ie, fold "(t.*).n" into "t.n".

regards, tom lane