A combined approach works if want to encode the exclusive constraint: CREATE TYP...

A combined approach works if want to encode the exclusive constraint:

    CREATE TYPE school_type AS ENUM ('college', 'high_school');
    CREATE TABLE schools (
      id SERIAL PRIMARY KEY,
      type school_type,
      unique (id, type)
    );
    CREATE TABLE colleges (
      id INTEGER NOT NULL,
      type school_type default 'college',
      check (type='college'),
      foreign key (id, type) references school(id, type)
    );

Ya, the syntax is annoying and repetitive. It would be nice if foreign key could be a literal to remove the extra column altogether. e.g.:

    foreign key (id, 'college') references school(id, type)