Find / Remove duplicates PostgreSQL

script.sql

CREATE TABLE customer (
  customer_id serial PRIMARY KEY,
  first_name VARCHAR ( 50 ) NOT NULL,
  last_name VARCHAR ( 50 ) NOT NULL,
  address VARCHAR ( 50 ) NOT NULL
)

INSERT INTO customer (first_name, last_name, address) values ('John', 'B', 'x Avenue');
INSERT INTO customer (first_name, last_name, address) values ('John', 'B', 'x Avenue');
INSERT INTO customer (first_name, last_name, address) values ('Maria', 'Pena', 'Cal St.');
INSERT INTO customer (first_name, last_name, address) values ('Maria', 'Pena', 'Cal St.');
INSERT INTO customer (first_name, last_name, address) values ('Maria', 'Pena', 'Cal St.');

SELECT COUNT(*)
FROM customer as a
WHERE a.customer_id IN
  (SELECT customer_id FROM
     (SELECT
      customer_id,
      ROW_NUMBER() OVER
        (PARTITION BY first_name, last_name, address
         ORDER BY customer_id) dup
    FROM customer) as c
    WHERE dup > 1);

--three records will be removed:

DELETE
FROM customer as a
WHERE a.customer_id IN
  (SELECT customer_id FROM
     (SELECT
      customer_id,
      ROW_NUMBER() OVER
        (PARTITION BY first_name, last_name, address
         ORDER BY customer_id) dup
    FROM customer) as c
    WHERE dup > 1);