Add primary key to PostgreSQL table only if it does not exist

Question

I have simple table creating script in Postgres 9.1. I need it to create the table with 2-attributes PK only if it does not exist.

CREATE TABLE IF NOT EXISTS "mail_app_recipients" (     "id_draft" Integer NOT NULL,     "id_person" Integer NOT NULL ) WITH (OIDS=FALSE); -- this is OK  ALTER TABLE "mail_app_recipients" ADD PRIMARY KEY IF NOT EXISTS ("id_draft","id_person"); -- this is problem since "IF NOT EXISTS" is not allowed. 

Any solution how to solve this problem? Thanks in advance.

Answer 1

You could do something like the following, however it is better to include it in the create table as a_horse_with_no_name suggests.

if NOT exists (select constraint_name from information_schema.table_constraints where table_name = 'table_name' and constraint_type = 'PRIMARY KEY') then  ALTER TABLE table_name   ADD PRIMARY KEY (id);  end if;