On Fri, Dec 17, 2004 at 11:10:12AM -0000, Filip Wuytack wrote: > Is it possible to have a sequence (as a multirow prim key), where sequence > (id) only increase per group of data (grp). > > E.g. > +--------+----+---------+ > | grp | id | name | > +--------+----+---------+ > | fish | 1 | lax | > | mammal | 1 | dog | > | mammal | 2 | cat | > | mammal | 3 | whale | > | bird | 1 | penguin | > | bird | 2 | ostrich | > +--------+----+---------+
PostgreSQL's sequences are simply number generators that return a unique value. If you want to generate keys in the manner you describe, then you could use a trigger to calculate what the next id should be. You'd probably have to lock the table to ensure that the operation works when multiple transactions are updating at the same time. Take a look at the "Triggers" chapter in the documentation, as well as the "Trigger Procedures" section of the "PL/pgSQL - SQL Procedural Language" chapter and the "Concurrency Control" chapter. -- Michael Fuhr http://www.fuhr.org/~mfuhr/ ---------------------------(end of broadcast)--------------------------- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
