text: create extension if not exists "uuid-ossp";
  
  create table if not exists "group"
  (
      id                varchar
          constraint group_pk primary key                 default uuid_generate_v4(),
      name              varchar                  not null,
      ref               varchar                  not null
          constraint group_ref_unique unique,
      creation_datetime timestamp with time zone not null default now()
  );
  