2012/3/11 Tom Lane <tgl@sss.pgh.pa.us>:
> Pavel Stehule <pavel.stehule@gmail.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.)
in this case the constant is forwarded to result without any change,
so it can be UNKNOWN.
Pavel
>
> regards, tom lane
