はせがわです。

例です。

EXPLAIN
select * 
>from 顧客マスタ 
order by ユーザー番号 desc limit 8;

+------------+-------+---------------+------+---------+------+----------------------------+
| table      | type  | possible_keys | key  | key_len | ref  | Extra                      |
+------------+-------+---------------+------+---------+------+----------------------------+
| 顧客マスタ | range | 性別          | 性別 |       2 | NULL | where used; Using filesort |
+------------+-------+---------------+------+---------+------+----------------------------+
=>超低速

EXPLAIN
select * 
>from 顧客マスタ 
where 性別='男' 
order by ユーザー番号 desc limit 8;
+------------+-------+---------------+---------+---------+------+-------+-------+
| table      | type  | possible_keys | key     | key_len | ref  | rows  | Extra |
+------------+-------+---------------+---------+---------+------+-------+-------+
| 顧客マスタ | index | NULL          | PRIMARY |       4 | NULL | 95095 |       |
+------------+-------+---------------+---------+---------+------+-------+-------+
=>高速



Using filesort
がなぜでるのだろう・・・

3.22では問題ないのに。