NikhilS <nikkhils@gmail.com> writes:
> To allow both of the above to hold, I think the subselect will have to be
> treated like a EXPR_SUBLINK subquery. I was wondering if we have a similar
> mechanism for plain selects/subselects to check and restrict their output to
> a single row.
No. Offhand I think you'd either need to relax EXPR_SUBLINK to allow
multiple output columns, or invent a ROW_SUBLINK SubLinkType that is
just like EXPR_SUBLINK except for allowing multiple output columns.
The latter would probably be less likely to break other things...
regards, tom lane