Had a need to drop a Foreign Key Constraint in PostgreSQL 8.x today, and this is how you do it:
database=> \d table_name;
Table "public.table_name"
Column | Type | Modifiers
------------------+------------------------+-----------
id | integer |
field | character varying(20) |
field_description | character varying(150) |
Indexes:
[..]
Foreign-key constraints:
"table_name_id_fkey" FOREIGN KEY (id) REFERENCES other_table(id) ON DELETE CASCADE
database=> ALTER TABLE table_name DROP CONSTRAINT "table_name_id_fkey";
ALTER TABLE
database=>
As simple as that. The name of the constraint is shown when describing the table with \d under “Foreign-key constraints”, and you simply do an ALTER statement to drop the constraint.