limit offset,n揭秘_MySQL

今天利用limit offset,n从一个表中分批导出数据的时候，总比原表少那么几条记录，创建一个小表做测试才发现其中的奥秘：

mysql> select * from sss1;<br>+----+------+------+<br>| id | name | c_id |<br>+----+------+------+<br>|  1 | aaa  |    1 | <br>|  2 | bbb  |    2 | <br>|  3 | ccc  |    3 | <br>|  4 | ddd  |    1 | <br>|  5 | eee  |    4 | <br>|  6 | ffff |    6 | <br>|  7 | NULL |    0 | <br>|  8 | NULL |    0 | <br>|  9 | NULL |    0 | <br>| 10 | ssss |    0 | <br>| 11 | ooo  |    0 | <br>| 12 | 234  |    0 | <br>+----+------+------+<br>12 rows in set (0.00 sec)<br><br>mysql> select * from sss1 limit 0,3;<br>+----+------+------+<br>| id | name | c_id |<br>+----+------+------+<br>|  1 | aaa  |    1 | <br>|  2 | bbb  |    2 | <br>|  3 | ccc  |    3 | <br>+----+------+------+<br>3 rows in set (0.00 sec)<br><br>mysql> select * from sss1 limit 4,6; <br>+----+------+------+<br>| id | name | c_id |<br>+----+------+------+<br>|  5 | eee  |    4 | <br>|  6 | ffff |    6 | <br>|  7 | NULL |    0 | <br>|  8 | NULL |    0 | <br>|  9 | NULL |    0 | <br>| 10 | ssss |    0 | <br>+----+------+------+<br>6 rows in set (0.00 sec)

看明白了吗？

如果有offset的话，就会从offset+1条开始显示，越过第offset条，所以分批后我才会少几条记录，刚好是我的offset点，解决办法：offset 和上一条的n保持一致就行了：

mysql> select * from sss1;<br>+----+------+------+<br>| id | name | c_id |<br>+----+------+------+<br>|  1 | aaa  |    1 | <br>|  2 | bbb  |    2 | <br>|  3 | ccc  |    3 | <br>|  4 | ddd  |    1 | <br>|  5 | eee  |    4 | <br>|  6 | ffff |    6 | <br>|  7 | NULL |    0 | <br>|  8 | NULL |    0 | <br>|  9 | NULL |    0 | <br>| 10 | ssss |    0 | <br>| 11 | ooo  |    0 | <br>| 12 | 234  |    0 | <br>+----+------+------+<br>12 rows in set (0.00 sec)<br><br>mysql> select * from sss1 limit 0,3;<br>+----+------+------+<br>| id | name | c_id |<br>+----+------+------+<br>|  1 | aaa  |    1 | <br>|  2 | bbb  |    2 | <br>|  3 | ccc  |    3 | <br>+----+------+------+<br>3 rows in set (0.00 sec)<br><br>mysql> select * from sss1 limit 3,6; <br>+----+------+------+<br>| id | name | c_id |<br>+----+------+------+<br>|  4 | ddd  |    1 | <br>|  5 | eee  |    4 | <br>|  6 | ffff |    6 | <br>|  7 | NULL |    0 | <br>|  8 | NULL |    0 | <br>|  9 | NULL |    0 | <br>+----+------+------+<br>6 rows in set (0.00 sec)