Re: datatype of constant is not propagated into aggregate query

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> postgres=# insert into t1 select distinct '2001-01-01', 1 from
> generate_series(1,3);
> ERROR: column "d" is of type date but expression is of type text
> LINE 1: insert into t1 select distinct '2001-01-01', 1 from generate...
> ^
> HINT: You will need to rewrite or cast the expression.

The DISTINCT forces the sub-SELECT to decide on a type for the constant
(so that it can pick a semantics for DISTINCT-ing). And it chooses text
by default. This is maybe not terribly convenient, but I'm not sure it
would be a good idea at all for a surrounding INSERT to change the
semantics of a SELECT. Even discounting the implementation
difficulties, I don't think that'd satisfy the POLA.

(We do have a hack for adjusting the type if what the sub-select returns
is still of type UNKNOWN; that's safe because it implies that the
sub-select does not care about the type of the result column.)

regards, tom lane