In my PostgreSQL database I have a unique index created this way:
CREATE UNIQUE INDEX ON USING btree (my_column)
Assume you have the following:
Indexes:
"feature_pkey" PRIMARY KEY, btree (id, f_id)
"feature_unique" UNIQUE, btree (feature, f_class)
"feature_constraint" UNIQUE CONSTRAINT, btree (feature, f_class)
To drop the UNIQUE CONSTRAINT, you would use ALTER TABLE:
ALTER TABLE feature DROP CONSTRAINT feature_constraint;
To drop the PRIMARY KEY, you would also use ALTER TABLE:
ALTER TABLE feature DROP CONSTRAINT feature_pkey;
To drop the UNIQUE [index], you would use DROP INDEX:
DROP INDEX feature_unique;