Andres Freund <andres@anarazel.de> writes: > I'm a bit worried about a case like:
> CREATE FUNCTION yell(int, int) > RETURNS int > IMMUTABLE > LANGUAGE SQL AS $$ > SELECT CASE WHEN $1 != 0 THEN 17 / $2 ELSE NULL END > $$;
> EXPLAIN SELECT yell(g.i, 0) FROM generate_series(1, 10) g(i);
> I don't think the parameters here would have been handled before > inlining, right?
Ah, I see what you mean. Yeah, that throws an error today, and it still would with the patch I was envisioning (attached), because inlining does Param substitution in a different way. I'm not sure that we could realistically fix the inlining case with this sort of approach.
I think this bears out the comment I made before that this approach still leaves us with a very complicated behavior. Maybe we should stick with the previous approach, possibly supplemented with a leakproofness exception.
I am actually not so sure this is a good idea. Here are two doubts I have.
1. The problem of when a given SQL expression is evaluated crops up in a wide variety of different contexts and, worst case, causes far more damage than queries which always error. Removing the lower hanging fruit while leaving cases like:
select lock_foo(id), * from foo where somefield > 100; -- which rows does lock_foo(id) run on? Does it matter?
is going to legitimize these complaints in a way which will be very hard to do unless we also want to eventually be able to specify when volatile functions may be run. The two cases don't look the same but they are manifestations of the same problem which is that when you execute a SQL query you have no control over when expressions are actually run.
2. The refusal to fold immutables within case statements here mean either we do more tricks to get around the planner if we hit a pathological cases in performance. I am not convinced this is a net win.
If we go this route, would it be too much to ask to allow a GUC variable to preserve the old behavior?
