Slide 9
Slide 9 text
再現してみた
mysql> insert into types values
(4,'typeD'),(5,'typeE'),(6,'typeF'),(7,'typeG'),(8,'typeH'),(9,'typeI'),(10,'typeJ');
Query OK, 7 rows affected (0.03 sec)
Records: 7 Duplicates: 0 Warnings: 0
mysql> explain select * from mytable left join types on mytable.type_id = types.id;
+----+-------------+---------+------------+--------+---------------+---------+---------+----------------------+-----
---+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows
| filtered | Extra |
+----+-------------+---------+------------+--------+---------------+---------+---------+----------------------+-----
---+----------+-------+
| 1 | SIMPLE | mytable | NULL | ALL | NULL | NULL | NULL | NULL |
488245 | 100.00 | NULL |
| 1 | SIMPLE | types | NULL | eq_ref | PRIMARY | PRIMARY | 4 | kubo.mytable.type_id |
1 | 100.00 | NULL |
+----+-------------+---------+------------+--------+---------------+---------+---------+----------------------+-----
---+----------+-------+
2 rows in set, 1 warning (0.00 sec)