text: create table couplings
  (
      entity           text not null,
      coupled          text not null,
      degree           decimal,
      averageRevisions decimal,
      app_id           uuid not null
          constraint fk_couplings_app
              references apps
              on delete cascade
  );
  
  create index couplings_app_degree_revisions_idx
      on couplings (app_id, degree, averageRevisions);