text: CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    first_name VARCHAR(30),
    last_name VARCHAR(30),
    user_name VARCHAR(30) UNIQUE
  );
  INSERT INTO users (first_name, last_name, user_name) VALUES ('ivan', 'ivanov', 'ivan1');
  INSERT INTO users (first_name, last_name, user_name) VALUES ('ivan', 'ivanov', 'ivan2');
  INSERT INTO users (first_name, last_name, user_name) VALUES ('ivan', 'ivanov', 'ivan3');
  INSERT INTO users (first_name, last_name, user_name) VALUES ('ivan', 'ivanov', 'ivan4');
  
  CREATE TABLE calls (
    id SERIAL PRIMARY KEY,
    caller_id INTEGER,
    receiver_id INTEGER,
    duration INTEGER,
    call_date DATE
  );
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('1', '2', '3', now());
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('2', '3', '3', now());
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('4', '1', '3', now());
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('4', '3', '3', now());
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('3', '4', '3', now());
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('1', '1', '3', now());
  INSERT INTO calls (caller_id, receiver_id, duration, call_date) VALUES ('4', '3', '3', now());
  
  CREATE TABLE contracts (
    user_id INTEGER,
    id SERIAL PRIMARY KEY,
    tarrif_id INTEGER
  );
  INSERT INTO contracts (user_id, tarrif_id) VALUES ('1', '1');
  INSERT INTO contracts (user_id, tarrif_id) VALUES ('2', '1');
  INSERT INTO contracts (user_id, tarrif_id) VALUES ('3', '1');
  INSERT INTO contracts (user_id, tarrif_id) VALUES ('4', '1');
  