Update: The Solution!
Thanks to the help of oicu on #postgresql on Freenode, the following solution does what I want:
SELECT currval(relname) AS lastID
FROM pg_class
WHERE relname ~ '^TABLENAME_.+_seq$' AND relkind='S';Problem Overview
I want to write a function (in PL/Ruby for PostgreSQL) which performs an insert on a table, and returns the ID of the primary key/sequence for that table, if one exists.
I want this function to figure out on its own if the table's primary key is a sequence, and if so what it's name is (so I can use the currval() function).
Findings So Far
Last night DBhome_ pointed me to the pg_class and pg_attribute tables and offered the following rough code:
select a.attname, a.oid
from pg_attribute a, pg_class c
where c.relid = a.relid and c.relname ='tname'
order by a.oid
limit 1;Unfortunately this didn't work directly: pg_attribute doesn't have an oid column, and pg_class doesn't have a relid column. But it's a start! :)
Following are excerpts from the two tables which are hopefully in the correct range. Assume I want to find out if the t_clients table's primary key is a sequence, and if so I want to know the name of the sequence (which I suppose I can construct if I know the name of the primary key which is a sequence).
pg_class
pg_attribute
