Method is_ref_for_hash_join

sql/sql_select.h:709–709

  bool hash_join_is_possible();
  int make_scan_filter();
  bool is_ref_for_hash_join() { return is_hash_join_key_no(ref.key); }
  KEY *get_keyinfo_by_key_no(uint key) 
  {
    return (is_hash_join_key_no(key) ? hj_key : table->key_info+key);