On Wed, Jan 26, 2011 at 4:20 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> Considering the number of OTHER places we'd have to break backward >> compatibility, one more wouldn't bother me any, but apparently that's >> just me. > > Well, again, it'd be all right with me if we were going to get any > meaningful increment in functionality out of it, but we aren't. If you > add the column and the default in separate steps, you get the same > result and all the behavior is spec-compliant. > > There's some history here that you may not be familiar with --- we used > to have exactly this bug in regards to the mainline ALTER TABLE case. > Observe the results in PG 7.1: > > regression=# create table foo(f1 int); > CREATE > regression=# insert into foo values(1); > INSERT 3151259 1 > regression=# insert into foo values(2); > INSERT 3151260 1 > regression=# alter table foo add column f2 int default 2; > ALTER > regression=# select * from foo; > f1 | f2 > ----+---- > 1 | > 2 | > (2 rows) > > In 7.2 through 7.4 the ALTER failed instead: > regression=# alter table foo add column f2 int default 2; > ERROR: Adding columns with defaults is not implemented. > Add the column, then use ALTER TABLE SET DEFAULT. > > and by 8.0 we'd finally made it work per spec. But we got lots of flak > meanwhile from people who'd gotten used to the old behavior. So those > of us who were around then aren't eager to repeat that. The code you're > complaining about now was put in only a month after we got that problem > fixed, so the issue was plenty fresh in mind at the time.
Yeah, I wasn't aware of that. I'll go revert, but I think I'll also add a big fat comment, because this is entirely non-obvious, especially because we don't disallow the cases SET NOT NULL and ADD table_constraint, which have the same darn problem. Aren't people who are used to those cases going to be pretty surprised too? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
