Re: You might be able to move the set-returning function into a LATERAL FROM item.

Alexander Farber <alexander(dot)farber(at)gmail(dot)com> writes:
> I am trying to fetch a history/protocol of a game with:

> SELECT
> CASE WHEN JSONB_TYPEOF(tiles) = 'array' THEN
> JSONB_ARRAY_ELEMENTS(tiles) ELSE NULL END AS x

I think you could push the conditionality into a plpgsql function,
something like (untested)

create function jsonb_elements_if_array(j jsonb) returns setof jsonb as $$
begin
if jsonb_typeof(j) = 'array' then
return query select jsonb_array_elements(j);
end if;
end$$
strict immutable language plpgsql;

Note that this gives *no* elements, rather than a single NULL value,
if the input isn't an array --- but that seems to me to make more sense
than your existing code anyhow. If you disagree, add "else return next
null::jsonb".

regards, tom lane