How to find inherited tables programatically in PostgreSQL?

Question

I have a PostgreSQL 8.3 database where table inheritance is being used. I would like to get a list of all tables along with its schema name which is inherited from a base ta

Answer 1

It's important to note that one table can inherit multiple tables, and none of the solutions listed really expose that; they just walk down the tree of a single parent. Consider:

CREATE TABLE a();
CREATE TABLE b();
CREATE TABLE ab_() INHERITS (a,b);
CREATE TABLE ba_() INHERITS (b,a);
CREATE TABLE ab__() INHERITS (ab_);
CREATE TABLE ba__() INHERITS (ba_);
CREATE TABLE ab_ba_() INHERITS (ab_, ba_);
CREATE TABLE ba_ab_() INHERITS (ba_, ab_);

WITH RECURSIVE inh AS (
        SELECT i.inhparent::regclass, i.inhrelid::regclass, i.inhseqno FROM pg_catalog.pg_inherits i WHERE inhparent = 'a'::regclass
        UNION
        SELECT i.inhparent::regclass, i.inhrelid::regclass, i.inhseqno FROM inh INNER JOIN pg_catalog.pg_inherits i ON (inh.inhrelid = i.inhparent)
) SELECT * FROM inh;
 inhparent | inhrelid | inhseqno 
-----------+----------+----------
 a         | ab_      |        1
 a         | ba_      |        2
 ab_       | ab__     |        1
 ba_       | ba__     |        1
 ab_       | ab_ba_   |        1
 ba_       | ab_ba_   |        2
 ba_       | ba_ab_   |        1
 ab_       | ba_ab_   |        2
(8 rows)

Notice that b doesn't show up at all which is incorrect, as both ab_ and ba_ inherit b.

I suspect the "best" way to handle this would be a column that's text[] and contains (array[inhparent::regclass])::text for each table. That would give you something like

inhrelid   path
ab_        {"{a,b}"}
ba_        {"{b,a}"}
ab_ba_     {"{a,b}","{b,a}"}

While obviously not ideal, that would at least expose the complete inheritance path and allow you to access it with enough gymnastics. Unfortunately, constructing that is not at all easy.

A somewhat simpler alternative is not to include the full inheritance path at each level, only each tables direct parents. That would give you this:

inhrelid    parents
ab_         {a,b}
ba_         {b,a}
ab_ba_      {ab_,ba_}