Re: ? in explain query

Rajesh Kumar Mallah <mallah(at)trade-india(dot)com> writes:
> In the explain below are the references
> "outer"."?column2?" = "inner"."?column2?"
> Ok?

Yeah, those are variables that don't have any name because they don't
correspond exactly to table columns. It looks like the plan is
merge-joining (main.id)::text to (groups_1.instance)::text. At the
level of the scans it's possible to see the expressions involved, but
at the level of the join those are just Var references to the outputs
of the lower plan steps.

We could possibly alter EXPLAIN to print the referred-to expression
instead of faking up a name for the Var node, but this would make the
printout look like the expression was being recomputed at the upper
level, which it isn't.

regards, tom lane