Re: plan for function returning table combined with condition

Thierry Henrio <thierry.henrio@gmail.com> writes:
> I made a function out of this sql:

> create or replace function expand_shop_opening_times() returns table(id
> int, name text, day int, startt time, endt time)
> as $$
> select id, name, day::int, (value -> 0 ->> 0)::time as startt, (value -> 0
> ->> 1)::time as endt from (
>   select s.id, s.name, j.* from shops s cross join
> jsonb_each(s.opening_times) as j(day, value)
> ) t
> $$ language sql

> So I can use it like so (A):

> select id, name from expand_shop_opening_times() where id=1307;

> The plan for statement (A) is:

>  Function Scan on expand_shop_opening_times  (cost=0.25..12.75 rows=5
> width=36) (actual time=15.950..16.418 rows=7 loops=1)
>    Filter: (id = 1307)
>    Rows Removed by Filter: 10540
>  Planning Time: 0.082 ms
>  Execution Time: 16.584 ms

You want this SQL function to be inlined, but it isn't being.
I think the reason is that (by default) it's VOLATILE, and
inline_set_returning_function doesn't like that:

     * Forget it if the function is not SQL-language or has other showstopper
     * properties.  In particular it mustn't be declared STRICT, since we
     * couldn't enforce that.  It also mustn't be VOLATILE, because that is
     * supposed to cause it to be executed with its own snapshot, rather than
     * sharing the snapshot of the calling query.  We also disallow returning
     * SETOF VOID, because inlining would result in exposing the actual result
     * of the function's last SELECT, which should not happen in that case.

So try adding STABLE to the function definition.

(This could be better documented, perhaps.)

            regards, tom lane