Re: order by primary key slowly

[varky chan]

mysql> explain select id from user limit 1000000,10;
+----+-------------+-------+-------+---------------+-----------------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+-----------------+---------+------+---------+-------------+
| 1 | SIMPLE | user | index | NULL | invite_user_idx | 5 | NULL | 5465723 | Using index |
+----+-------------+-------+-------+---------------+-----------------+---------+------+---------+-------------+
1 row in set (0.51 sec)

mysql> explain select id from user order by id limit 1000000,10;
+----+-------------+-------+-------+---------------+---------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+---------+---------+------+---------+-------------+
| 1 | SIMPLE | user | index | NULL | PRIMARY | 4 | NULL | 1000010 | Using index |
+----+-------------+-------+-------+---------------+---------+---------+------+---------+-------------+
1 row in set (0.00 sec)

Actually, the table have another filed named invite_user_id with int type, and a index named invite_user_idx for it.