Форум пользователей MySQL

mysql> explain select elt(1, 'st',c.name,cc.code)='st' from city c left join cou
ntry cc on 1=0 where elt(1, 'st',c.name,null)='st' limit 1\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: c
   partitions: NULL
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 4188
     filtered: 100.00
        Extra: Using where
*************************** 2. row ***************************
           id: 1
  select_type: SIMPLE
        table: cc
   partitions: NULL
         type: index
possible_keys: NULL
          key: PRIMARY
      key_len: 3
          ref: NULL
         rows: 239
     filtered: 100.00
        Extra: Using where; Using index; Using join buffer (Block Nested Loop)
2 rows in set, 1 warning (0.03 sec)

mysql> explain select elt(1, 'st',c.name,cc.code)='st' from city c left join cou
ntry cc on 1=0 where elt(1, 'st',c.name,cc.code)='st' limit 1\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: NULL
   partitions: NULL
         type: NULL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: NULL
     filtered: NULL
        Extra: Impossible WHERE
1 row in set, 1 warning (0.00 sec)

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.9-log |
+-----------+