text: CREATE extension IF NOT EXISTS ltree;
  CREATE TABLE departments (
      id int NOT NULL PRIMARY KEY,
      name varchar(255) NOT NULL,
      struct ltree NOT NULL,
      deleted_at TIMESTAMP
  );
  CREATE UNIQUE INDEX departments_struct_idx ON departments (struct);
  CREATE TABLE user_department(
      user_id int NOT NULL,
      department_id int NOT NULL,
      PRIMARY KEY(user_id, department_id)
  );