Mike Mascari <mascarm(at)mascari(dot)com> writes:
> This is a really trivial question, but I'm curious. Why do
> subselects in target lists behave differently than simple queries?
> [lexus] insert into bar select '';
> INSERT 1319585 1
> [lexus] insert into bar select (select '') as key;
> ERROR: failed to find conversion function from "unknown" to
> character varying
The undecorated literal constant starts out marked as type UNKNOWN.
There is a hack to reinterpret it as the type of the destination
column in an INSERT context. The hack doesn't know anything about
looking inside subselects, though.
regards, tom lane