text: create table t_user(
    id_user int(11) primary key auto_increment,
    mail varchar(50) not null,
    name varchar(50) not null
  );
  create table t_group(
    id_group int(11) primary key auto_increment,
    id_user  int(11) 
  );
  create table t_message(
    id_group int(11) primary key auto_increment,
    id_user int(11),
    id_message int(11),
    message varchar(4000)
  );
  