text: -- https://github.com/kyleconroy/sqlc/issues/604
  CREATE TABLE users (
    user_id    INT PRIMARY KEY,
    city_id    INT -- nullable
  );
  CREATE TABLE cities (
    city_id    INT PRIMARY KEY,
    mayor_id   INT NOT NULL
  );
  CREATE TABLE mayors (
    mayor_id   INT PRIMARY KEY,
    full_name  TEXT NOT NULL
  );
  
  -- name: GetMayors :many
  SELECT
      user_id,
      mayors.full_name
  FROM users
  LEFT JOIN cities USING (city_id)
  INNER JOIN mayors USING (mayor_id);
  
  -- name: GetMayorsOptional :many
  SELECT
      user_id,
      cities.city_id,
      mayors.full_name
  FROM users
  LEFT JOIN cities USING (city_id)
  LEFT JOIN mayors USING (mayor_id);
  