Re: Explain and filter over subplans

Chantal Keller <chantal(dot)keller(at)universite-paris-saclay(dot)fr> writes:
> I would like "explain" to output formulas for filtering over
> subplans. Is it possible?

No, and that's been a to-do item for a long time.

Currently, EXPLAIN just ignores the "testexpr" field of SubPlan
nodes, which is what you are after. We could print it, if we
could figure out an intelligible representation. In the example
you give, the testexpr would probably render as "t.a >= $0"
where $0 represents the subplan's output column.

A very rough sketch, perhaps, is that instead of just
"(SubPlan 1)", we could print "(ALL t.a >= $0 FROM SubPlan 1)".
Some of the other SubLinkTypes might be harder to represent
in a way that makes sense to users.

I made a quick-hack patch to play with, if you're interested.

regards, tom lane