使用mysql中的limit offset,n从一个表中分批导出数据时，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，分享一下，供大家学习参考。
mysql> select * from sss1;
+----+------+------+
| id | name | c_id |
+----+------+------+
| 1 | aaa | 1 |
| 2 | bbb | 2 |
| 3 | ccc | 3 |
| 4 | ddd | 1 |
| 5 | eee | 4 |
| 6 | ffff | 6 |
| 7 | NULL | 0 |
| 8 | NULL | 0 |
| 9 | NULL | 0 |
| 10 | ssss | 0 |
| 11 | ooo | 0 |
| 12 | 234 | 0 |
+----+------+------+
12 rows in set (0.00 sec)
mysql> select * from sss1 limit 0,3;
+----+------+------+
| id | name | c_id |
+----+------+------+
| 1 | aaa | 1 |
| 2 | bbb | 2 |
| 3 | ccc | 3 |
+----+------+------+
3 rows in set (0.00 sec)
mysql> select * from sss1 limit 4,6;
+----+------+------+
| id | name | c_id |
+----+------+------+
| 5 | eee | 4 |
| 6 | ffff | 6 |
| 7 | NULL | 0 |
| 8 | NULL | 0 |
| 9 | NULL | 0 |
| 10 | ssss | 0 |
+----+------+------+
6 rows in set (0.00 sec)
看明白了没有？
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;
+----+------+------+
| id | name | c_id |
+----+------+------+
| 1 | aaa | 1 |
| 2 | bbb | 2 |
| 3 | ccc | 3 |
| 4 | ddd | 1 |
| 5 | eee | 4 |
| 6 | ffff | 6 |
| 7 | NULL | 0 |
| 8 | NULL | 0 |
| 9 | NULL | 0 |
| 10 | ssss | 0 |
| 11 | ooo | 0 |
| 12 | 234 | 0 |
+----+------+------+
12 rows in set (0.00 sec)
mysql> select * from sss1 limit 0,3;
+----+------+------+
| id | name | c_id |
+----+------+------+
| 1 | aaa | 1 |
| 2 | bbb | 2 |
| 3 | ccc | 3 |
+----+------+------+
3 rows in set (0.00 sec)
mysql> select * from sss1 limit 3,6;
+----+------+------+
| id | name | c_id |
+----+------+------+
| 4 | ddd | 1 |
| 5 | eee | 4 |
| 6 | ffff | 6 |
| 7 | NULL | 0 |
| 8 | NULL | 0 |
| 9 | NULL | 0 |
+----+------+------+
6 rows in set (0.00 sec)