On Wed, Dec 14, 2005 at 06:26:23PM +0100, Jost Degenhardt wrote:
> I have the following problem: My database consists of several tables
> that are inherited from each other with one single supertable on top of
> that hierarchy. Now I would like to select a single row in that
> supertable and want to find out to which of the tables in the hierarchy
> it belongs.
http://www.postgresql.org/docs/8.1/interactive/ddl-inherit.html
In some cases you may wish to know which table a particular row originated from. There is a system column called
tableoidin each table which can tell you the originating table:
http://www.postgresql.org/docs/8.1/interactive/ddl-system-columns.html
tableoid
The OID of the table containing this row. This column is particularly handy for queries that select from
inheritancehierarchies (see Section 5.8), since without it, it's difficult to tell which individual table a row
camefrom. The tableoid can be joined against the oid column of pg_class to obtain the table name.
Here's an example; instead of getting the table name via a join
with pg_class it uses a cast to regclass:
CREATE TABLE parent (t text);
CREATE TABLE child1 () INHERITS (parent);
CREATE TABLE child2 () INHERITS (parent);
INSERT INTO child1 VALUES ('one');
INSERT INTO child2 VALUES ('two');
SELECT tableoid::regclass, * FROM parent;tableoid | t
----------+-----child1 | onechild2 | two
(2 rows)
--
Michael Fuhr
