How to delete/drop a constraint in PostgresSQL
This article will show you how to drop a contraint, such as a foreign key contraint, on a PostgresSQL 8.x database.
Login to the PostgresSQL command-line interface
psql -U [username] [database_name]
Show a list of constraints on a particular table
\d [table_name]
To Delete (or Drop) the constraint, use the command:
ALTER TABLE [table_name] DROP CONSTRAINT [constraint_name];