schema prefixes in default values (was RE: removing "serial" from table definitions).

Marc Mamin <M(dot)Mamin(at)intershop(dot)de> writes:
> > Yes, I undersand that serial is just a hint at table creation time, but is there a place in catalog where we can see if the table was created using 'serial' ?
>
> No. Where the docs say "these are equivalent", they mean that very literally.
>
> > The difference we see between the source and target database is that a schema prefix is displayed with the sequence on one side, and not on the other..
>
> This likely has to do with the search_path settings being different in the sessions inspecting the two DBs. I do not think it is related to serial-ness at all, it's just the normal behavior of regclass_out for the OID constant that's the argument of nextval().
>
> regards, tom lane

Hello,
it seems that our problem had nothing to do with serial, but with the way schema prefixes are handled in column default values.

pg_attrdef.adsrc:
filled when the defaut value is defined. contains a schema prefix only when required at this creation time. Is constant afterwards.

pg_get_expr(adbin, adrelid)
the returned expession is dynamic: the schema prefix is returned only when the sequence schema is not part of the current search_path.

This behavior is understandable but it make it uncomfortable to compare table definitions between different sources.
Moreover a pg_dump->restore might in some cases modify the value of pg_attrdef.adsrc

best regards,

Marc Mamin

as test:

set search_path='admin';

create table foo1 (n1 serial);

set search_path='oms';

create table admin.foo2 (n2 serial);

select a.attname, ad.adsrc, pg_get_expr(adbin, adrelid)
FROM pg_attribute a
JOIN pg_attrdef ad ON (a.attnum=ad.adnum and a.attrelid=ad.adrelid)
WHERE a.attrelid IN (Select oid from pg_class where relname in('foo1','foo2'));

n1 nextval('foo1_n1_seq'::regclass) nextval('admin.foo1_n1_seq'::regclass)
n2 nextval('admin.foo2_n2_seq'::regclass) nextval('admin.foo2_n2_seq'::regclass)

set search_path='admin';

select a.attname, ad.adsrc, pg_get_expr(adbin, adrelid)
FROM pg_attribute a
JOIN pg_attrdef ad ON (a.attnum=ad.adnum and a.attrelid=ad.adrelid)
WHERE a.attrelid IN (Select oid from pg_class where relname in('foo1','foo2'));

n1 nextval('foo1_n1_seq'::regclass) nextval('foo1_n1_seq'::regclass)
n2 nextval('admin.foo2_n2_seq'::regclass) nextval('foo2_n2_seq'::regclass)