CREATE TABLE users (
  uid SERIAL NOT NULL,
  login VARCHAR(20) NOT NULL,
  pass VARCHAR(255) NOT NULL,
  fullname VARCHAR(255) NOT NULL DEFAULT '',
  email VARCHAR(255) NOT NULL DEFAULT '',
  PRIMARY KEY  (uid),
  UNIQUE (login)
);
 
CREATE TABLE groups (
  gid SERIAL NOT NULL,
  name VARCHAR(50) NOT NULL,
  PRIMARY KEY  (gid),
  UNIQUE (name)
);
 
CREATE TABLE usergroup (
  uid INTEGER NOT NULL REFERENCES users, 
  gid INTEGER NOT NULL REFERENCES groups,
  PRIMARY KEY  (uid,gid)
);