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I have three tables: organization, organization_teams and org_users. Here organization_teams is inherited from organization. So suppose if a record is added in organizations_teams it will get the organization table id as value for id column in organization_teams.

org_users has foreign key on id column of organization. Now when I try to insert data in org_users it giving me error as below

insert or update on table "org_users" violates foreign key constraint "org_users_organizations"
DETAIL:  Key (org_id)=(12) is not present in table "organizations"

Why?

Craig Ringer
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Supriya Pansare
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  • No. Sequences are not inherited. – frlan Jun 23 '14 at 07:17
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    This is known caveat: *A serious limitation of the inheritance feature is that indexes (including unique constraints) and foreign key constraints only apply to single tables, not to their inheritance children* http://www.postgresql.org/docs/current/static/ddl-inherit.html#DDL-INHERIT-CAVEATS – pozs Jun 23 '14 at 07:18
  • i already have some organizations in Organization tables and some in organization_teams,So org_user have foreign key on organizations. – Supriya Pansare Jun 23 '14 at 07:31

3 Answers3

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It's covered in the user manual.

The short version: you can use foreign keys, or table inheritance, but not both. This isn't inherently impossible, it's just that it's technically quite difficult to implement unique indexes that span inherited tables in PostgreSQL in a fast, reliable manner. Without that, you can't have a useful foreign key. Nobody's successfully implemented it well enough for a patch adding support to be accepted into PostgreSQL yet.

A foreign key can point to a table that is part of an inheritance hierarchy, but it'll only find rows in that table exactly. Not in any parent or child tables. To see which rows the foreign key sees, do a SELECT * FROM ONLY thetable. The ONLY keyword means "ignoring inheritance" and that's what the foreign key lookup will do.

Craig Ringer
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  • Would it be 'safe' to only apply foreign keys at the 'leaf' tables of a table inheritance hierarchy? – Andrew Wolfe Dec 23 '15 at 21:03
  • @AndrewWolfe If referencing and referenced tables are partitioned on the same key you can have FKs between corresponding partitions. That's about all. – Craig Ringer Dec 24 '15 at 02:07
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The only workaround i have found is:

  1. create function returning trigger for checking existence of some id in inherited table
  2. create a constraint trigger instead of FK
shcherbak
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Completely agree with @Craig Ringer, we can't use foreign keys along with inheritance.

But if we are sure that we are going to insert correct data, and we want to use foreign key in org_users, we can do one thing.

We can create a child table of org_users say org_users_child (with no foreign key) as below

CREATE TABLE org_users_child () INHERITS (org_users);

Now we can insert data in this child table.

Now if we query over org_users table, we can find desired results.

Anil Agrawal
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