Re: Problem with index not being chosen inside PL/PgSQL function...

"Weber, Geoffrey M." <Geoffrey(dot)Weber(at)mcleodusa(dot)com> writes:
> Hmm - good question! However, it is - both the id and
> not_displayed_id are INTEGERs.

Well, in that case it must be a statistics issue --- does the indexed
column have a badly skewed distribution?

You could investigate how many rows the planner thinks will be fetched
via

PREPARE foo(int) AS
SELECT ah.* FROM alert ah where ( (ah.replaced_by_id = '0') AND (not_displayed_id = $1 ) ) ORDER BY replaced_by_id, not_displayed_id;

EXPLAIN EXECUTE foo(42);

which will set up exactly the same planning situation as occurs in the
plpgsql function: no knowledge of the exact value being compared to.

regards, tom lane