CREATE TABLE hubs (
    id INTEGER NOT NULL PRIMARY KEY,
    default_location_id INTEGER NOT NULL DEFAULT -1,
    alias VARCHAR(40) NOT NULL UNIQUE,
    local INTEGER UNIQUE,
    hash VARCHAR,
    num_updates INTEGER,
    FOREIGN KEY (id) REFERENCES topics(id) ON DELETE CASCADE,
    FOREIGN KEY (id,default_location_id)
        REFERENCES hub_locations(hub_id,id)
        DEFERRABLE INITIALLY DEFERRED,
    CONSTRAINT local_constraint CHECK (
        local = 1 OR local IS NULL
    )
);