sqltoerdiagram.com: ER-диаграмма из SQL DDL

CREATE TABLE contacts (
  id INT PRIMARY KEY, first_name VARCHAR(50) NOT NULL,
  last_name VARCHAR(50) NOT NULL, email VARCHAR(100) UNIQUE
);
CREATE TABLE phone_numbers (
  id INT PRIMARY KEY,
  contact_id INT NOT NULL REFERENCES contacts(id),
  type VARCHAR(20) NOT NULL, number VARCHAR(20) NOT NULL
);
CREATE TABLE groups (id INT PRIMARY KEY, name VARCHAR(50) NOT NULL);
CREATE TABLE contact_groups (
  contact_id INT NOT NULL REFERENCES contacts(id),
  group_id   INT NOT NULL REFERENCES groups(id),
  PRIMARY KEY (contact_id, group_id)
);