Violation of uniqueness in primary key when using inheritance

I’m using inheritance in PostgreSQL but there is a big problem while using it. I have a Parent table and 2 Child Tables and I don’tknow how to insert a data in these tables. The uniqueness of Parent primary key become violated when I insert some data into child tables.

The parent table is:

CREATE TABLE Parent (
  pid int not null,
  pAttr1 int not null,
  primary key (pid)
)

The childs are:

CREATE TABLE child1 (
  ChAttr1 int not null
) INHERITS (Parent)

CREATE TABLE child2(
  ChAttr2 int not null
) INHERITS (Parent)

When i use these INSERTs :

INSERT into Parent values (1,10)
INSERT into Child1 values (1,20,30) --1 for pk, 20 for pAttr1 & 30 for ChAttr1
INSERT into Child2 values (1,50,60)

Then there are 3 entities with primary key of 1 in Parent table!!!

Answer

That is documented:

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. This is true on both the referencing and referenced sides of a foreign key constraint. Thus, in the terms of the above example:

• If we declared cities.name to be UNIQUE or a PRIMARY KEY, this would not stop the capitals table from having rows with names duplicating rows in cities. And those duplicate rows would by default show up in queries from cities.

If you SELECT * FROM parent, PostgreSQL effectively executes:

SELECT pid, pattr1 FROM parent
UNION ALL
SELECT pid, pattr1 FROM child1
UNION ALL
SELECT pid, pattr1 FROM child2;

You can look at the EXPLAIN output to verify that.