Re: Bad plan when join on function - Mailing list pgsql-performance

Zotov  wrote:

> select c.id from OneRow c join abstract a on a.id=AsInteger(c.id)

> Why SeqScan???

Because you don't have an index on AsInteger(c.id).

If your function is IMMUTABLE (each possible combination of input
values always yields the same result), and you declare it such, then
you can index on the function, and it will perform at a speed similar
to the other example.

-Kevin