Constraint for relation already exists

Constraint for relation already exists

The cause of error: There is already a constraint created with the same name.
Check the constraint name or drop the existing constraint.

Error message example

ALTER TABLE test.customers 
ADD CONSTRAINT fk_address 
FOREIGN KEY (address_id) 
REFERENCES test.customer_address (id);  

Messages

ERROR: constraint “fk_address” for relation “customers” already exists