Re: domain cast in parameterized vs. non-parameterized query

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> 2017-12-20 23:41 GMT+01:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>> Hm, scratch that --- experimentation shows that the parser still produces
>> a CoerceToDomain node in that case, not a literal of the domain type.

> Why the rewrite doesn't reduce it? Or why parser does it?

Because ALTER DOMAIN can change what would be a valid value.

regression=# create domain myd as int;
CREATE DOMAIN
regression=# create view v1 as select 0::myd as c1;
CREATE VIEW
regression=# select * from v1;
c1
----
0
(1 row)

regression=# alter domain myd add check (value > 0);
ALTER DOMAIN
regression=# select * from v1;
ERROR: value for domain myd violates check constraint "myd_check"

If the view's expression had been reduced to just a Const when it
was stored, we'd not notice that the value is no longer valid for
the domain. So CoerceToDomain is always postponed till runtime.

regards, tom lane