Mark Dilger <mark.dilger@enterprisedb.com> writes:
> I haven't studied the behavior of char(n) on other RDBMS products. I'd be curious if the SQL spec says anything that
we'reviolating in this regard.
It's not a great approximation to the spec. Postgres views trailing
spaces in a char(n) value as always being semantically insignificant,
where I think the spec treats them as insignificant only for purposes of
comparisons. Even more to the point, the spec considers that PAD SPACE
is an attribute of *collations* not data types. Back in the day we
didn't have collations, so the only way to even approximate that
behavior was to make it a data type property. Now that we do have
collations, it'd be conceivable to reimplement all this in something
closer to the way the spec describes it. But it'd be a lot of work,
and I'm not sure we'd accept such a patch even if somebody wrote it.
It'd almost inevitably break applications that are relying on the
existing behavior.
> I tend to think of char(n) as a misfeature and avoid using it.
Yeah, that. I haven't seen any reason to use char(n) rather than
varchar(n) since punched cards stopped being a thing. So it's hard
to summon the motivation to do a lot of work on that data type.
Perhaps somebody else will feel more motivated, but nobody's stepped
forward, and I wouldn't counsel holding your breath for it.
regards, tom lane