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In PostgreSQL, a table can inherit from zero or more other tables, and a query can reference either all rows of a table or all rows of a table plus all of its descendant tables.For example, the following query finds the names of all cities, including state capitals, that are located at an altitude over 500 feet:

CREATE TABLE cities (    name            text,    population      float,    altitude        int     -- in feet);CREATE TABLE capitals (    state           char(2)) INHERITS (cities);SELECT name, altitude    FROM cities    WHERE altitude > 500;

In some cases you might wish to know which table a particular row originated from. There is a system column called tableoid in each table which can tell you the originating table:

SELECT c.tableoid, c.name, c.altitudeFROM cities cWHERE c.altitude > 500; tableoid |   name    | altitude----------+-----------+----------   139793 | Las Vegas |     2174   139793 | Mariposa  |     1953   139798 | Madison   |      845

By doing a join with pg_class you can see the actual table names:

SELECT p.relname, c.name, c.altitudeFROM cities c, pg_class pWHERE c.altitude > 500 AND c.tableoid = p.oid;

Another way to get the same effect is to use the regclass pseudo-type, which will print the table OID symbolically:

SELECT c.tableoid::regclass, c.name, c.altitudeFROM cities cWHERE c.altitude > 500;

Inheritance does not automatically propagate data from INSERT or COPY commands to other tables in the inheritance hierarchy. In our example, the following INSERT statement will fail:

INSERT INTO cities (name, population, altitude, state)VALUES ('Albany', NULL, NULL, 'NY');

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