Bryce Nesbitt <[EMAIL PROTECTED]> writes:
> I got bit by this to be sure, but is it a bug?  I guess I'd hoped for a
> warning at the critical step (see "poof" below):

> create table tester (one int, two int, three int);
> alter table only tester add constraint no_dupes unique (one, two, three);
> ...
> alter table tester drop column old_three;
> \d tester;                                    -- poof, the constraint is
> gone with no warning

I don't think the renaming is relevant: you get the same with

regression=# create table tester (one int, two int, three int, unique 
(one,two,three));
NOTICE:  CREATE TABLE / UNIQUE will create implicit index "tester_one_key" for 
table "tester"
CREATE TABLE
regression=# alter table tester drop column three;
ALTER TABLE
regression=# \d tester
    Table "public.tester"
 Column |  Type   | Modifiers 
--------+---------+-----------
 one    | integer | 
 two    | integer | 

regression=# 

It does seem like this is wrong, in view of SQL92's statement about
ALTER TABLE DROP COLUMN:

         4) If RESTRICT is specified, then C shall not be referenced in
            the <query expression> of any view descriptor or in the <search
            condition> of any constraint descriptor other than a table con-
            straint descriptor that contains references to no other column
            and that is included in the table descriptor of T.

IOW we should only allow unique constraints to be auto-dropped if
they reference just the one single column.  Ick.

                        regards, tom lane

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