Default value of column not respecting character length or domain restraints.

"Justin Dearing" <zippy1981@gmail.com> writes:

It seems I can feed a default value to a domain that won't fit in the
underlying base type. I have the domain html_colors as so:

CREATE DOMAIN html_color AS char(7) CHECK (VALUE ~ '^#[A-Fa-f0-9]{6}$');

I then defined a column of html_colors as so:
ALTER TABLE users ALTER COLUMN profile_color SET DEFAULT '#FFFFRFF';

This worked fine and I didn't notice it until I added arecord to the
users table and got the error:
ERROR: value too long for type character(7).

This behavior seems undesirable to me. Is this a known bug or is there
a reason for this?

Well, the default isn't checked against constraints until it's used
at runtime.  This is appropriate in a number of situations because
time-varying defaults are not uncommon (eg "default now()" for a
timestamp column).  Also, defaults with side effects are not uncommon
--- think "default nextval('seq')" for a serial --- and causing those
side-effects to happen at CREATE TABLE time seems undesirable.

In short, I understand your annoyance, but the cure seems worse than
the disease. It's not like you won't find out soon enough if you
establish a constant default that doesn't meet your constraints.

regards, tom lane