Potential bug in ALTER TABLE?

Jeroen Ruigrok/asmodai <asmodai@wxs.nl> writes:

just want to verify first with you guys before dumping it on the bugs
list. Most likely I am just being silly here or something.

The ALTER ADD CONSTRAINT form creates a table constraint, ie, one that's
not attached to any particular column. If you write the constraint in
the CREATE TABLE as a table constraint, then you get the same result as
with ALTER ADD CONSTRAINT.

regression=# create table blah (name TEXT, CHECK (name IN ('blah', 'bleh')));
CREATE TABLE
regression=# \d blah
Table "public.blah"
Column | Type | Modifiers
--------+------+-----------
name | text |
Check constraints:
"$1" CHECK ((name = 'blah'::text) OR (name = 'bleh'::text))

If you don't like the automatically generated name, assign your own...

regression=# ALTER TABLE blah ADD CONSTRAINT fooey CHECK (name IN ('blah', 'bleh'));
ALTER TABLE
regression=# \d blah
Table "public.blah"
Column | Type | Modifiers
--------+------+-----------
name | text |
Check constraints:
"$1" CHECK ((name = 'blah'::text) OR (name = 'bleh'::text))
"fooey" CHECK ((name = 'blah'::text) OR (name = 'bleh'::text))

regards, tom lane

Jeroen Ruigrok/asmodai wrote:

Hi,

just want to verify first with you guys before dumping it on the bugs
list. Most likely I am just being silly here or something.

Take this:

create table blah (name TEXT CHECK (name IN ('blah', 'bleh')));
test=# \d blah
Table "public.blah"
Column | Type | Modifiers
--------+------+-----------
name | text |
Check constraints: "blah_name" ((name = 'blah'::text) OR (name = 'bleh'::text))

As we would expect PostgreSQL to do. The constraint has an
automatically assigned name.

Now, to continue:

ALTER TABLE blah DROP CONSTRAINT blah_name;
ALTER TABLE blah ADD CHECK (name IN ('blah', 'bleh'));
test=# \d blah
Table "public.blah"
Column | Type | Modifiers
--------+------+-----------
name | text |
Check constraints: "$1" ((name = 'blah'::text) OR (name = 'bleh'::text))

And this time around PostgreSQL doesn't assign an automatic name.
Well, it depends on what you call a name, but $1, $2, and so on isn't
quite descriptive. Is this an oversight or am I missing some subtle
thing here?

You can name it yourself:

ALTER TABLE blah ADD CONSTRAINT blurfl CHECK (name IN ('blah', 'bleh'));

I do this a lot.

I agree the autogenerated names are less than pretty.

cheers

andrew