Method check_only_first_match

sql/sql_select.h:649–654

    return is_first_inner_for_outer_join() || first_sj_inner_tab == this ; 
  }
  bool check_only_first_match()
  {
    return is_inner_table_of_semi_join_with_first_match() ||
           (is_inner_table_of_outer_join() &&
            table->reginfo.not_exists_optimize);
  }
  bool is_last_inner_table()
  {
    return (first_inner && first_inner->last_inner == this) ||