xxxxxxxxxx
// NO NEED to disable or delete unique index!
// just override the UNIQUE index with another one!
Schema::table('users', function (Blueprint $table) {
$table->unique(['user_id', 'role_id', 'department_id'],
'user_roles_user_id_role_id_department_id_unique');
});
// user_id role_id department_id
//-----------------------------------------
// 1 1 1 success
// 1 1 1 fail
// 1 1 3 success