explain
根据上面提到的explain去比较，就可以得出结果了
mysql> explain select * from users limit 1000,20;
+----+-------------+-------+------+---------------+------+---------+------+--------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+--------+-------+
| 1 | SIMPLE | users | ALL | NULL | NULL | NULL | NULL | 169847 | |
+----+-------------+-------+------+---------------+------+---------+------+--------+-------+
1 row in set (0.00 sec)
mysql> explain select * from users where uid>1000 limit 20;
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
| 1 | SIMPLE | users | range | PRIMARY | PRIMARY | 4 | NULL | 84923 | Using where |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
1 row in set (0.00 sec)
mysql> explain select * from users where uid between 1000 and 1020;
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
| 1 | SIMPLE | users | range | PRIMARY | PRIMARY | 4 | NULL | 1 | Using where |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
1 row in set (0.00 sec)
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