Trying to modify a constraint in PostgreSQL

According to the correct manual (which is supplied by PostgreSQL, not by Oracle), there is no modify constraint available in the ALTER TABLE statement:

Here is the link to the correct manual:

http://www.postgresql.org/docs/current/static/sql-altertable.html

There is no ALTER command for constraints in Postgres. The easiest way to accomplish this is to drop the constraint and re-add it with the desired parameters. Of course any change of the constraint will be run against the current table data.

BEGIN;
ALTER TABLE t1 DROP CONSTRAINT ...
ALTER TABLE t1 ADD CONSTRAINT ...
COMMIT;