Re: Index not used in functions in 7.0?

Kyle Bateman <kyle(at)actarg(dot)com> writes:
> create function summtr_ocpt2(text, int4) returns int4 as '
> select sum(tquant) from mtr_reg where to_proj = $2 and pnum = $1 and
> (status = \'open\' or status = \'clsd\' or status = \'prip\');
> ' language 'sql';

Ah, I've sussed it. The difference between the environment in your
function and the environment in a hand-entered query is that you've
declared $1 to be type 'text', whereas in the hand-entered query the
parser resolves the unknown-type string literal into type 'varchar'
to match the type of what it's being compared to. What you effectively
have inside the function is pnum::text = $1::text, and the planner is
not able to figure out that it can use a varchar index for that. If you
had written the hand-entered query as "... pnum = '1051'::text ..."
it wouldn't have been done with an indexscan either.

Best short-term solution is to declare the function as taking varchar
in the first place.

This behavior is a regression from 6.5, which handled implicit coercions
differently and could recognize the clause as indexable despite the
inserted coercion. I'll look into whether it's patchable for 7.0.1.
A proper fix might be too complex to risk patching into 7.0.1 though :-(
... might have to wait for 7.1.

regards, tom lane