text: CREATE TABLE IF NOT EXISTS challenge (
      id serial,
      title varchar(500),
      beginDate date,
      endDate date,
      PRIMARY KEY( id )
  );
  
  CREATE TABLE IF NOT EXISTS participant (
      profileId bigint,
      link varchar(500),
      username varchar(300),
      PRIMARY KEY( profileId )
  );
  
  CREATE TABLE IF NOT EXISTS challenge_participant (
      challenge_id int REFERENCES challenge (id) ON UPDATE CASCADE ON DELETE CASCADE ,
      participant_id int REFERENCES participant (profileId) ON UPDATE CASCADE ON DELETE CASCADE,
      CONSTRAINT challenge_participant_pkey PRIMARY KEY (challenge_id, participant_id) -- explicit pk
  );
  