Re: RFC: ALTER SYSTEM [...] COMMENT

Stephen Frost <sfrost(at)snowman(dot)net> writes:
> Having COMMENT ON accept a general query whose result is then cast to
> text and stored as the comment would allow this to be done, eg:

> COMMENT ON table IS (pg_get_comment('table') || ' new text');

Putting general subexpressions into utility statements has some
implementation issues. Plus, it's not really all that powerful.
It'd be better to invent inverse pg_get_comment and pg_set_comment
functions, then you could do bulk-update things like

select pg_set_comment('table', pg_get_comment('table') || ' more')
from pg_class where ...

The main thing lacking to make that into a real proposal would be
a way of naming the object the comment is for; but I think Alvaro's
already exposed something corresponding to ObjectAddress to SQL, no?

> We could also have new syntax along these lines, for this specific case:
> COMMENT ON table ADD ' new text';

Wouldn't have a big problem with that, as it'd address a common case
for not much work.

regards, tom lane