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mysql如何指定查询一张表的查询结果，如最后5行记录和最前5行记录
我们以student表为例，里面有三个字段：id,name,age，其中id为主健，为自增，里面共有10条记录，如下所示。
mysql> select  * from student;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | li   |   11 |
|  2 | zh   |   12 |
|  3 | chou |   13 |
|  4 | he   |   14 |
|  5 | lin  |   15 |
|  6 | ll   |   16 |
|  7 | chen |   17 |
|  8 | yu   |   18 |
|  9 | wu   |   19 |
| 10 | xie  |   20 |
+----+------+------+
10 rows in set (0.00 sec)

1、查询第一行记录
select * from student limit 1;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | li   |   11 |
+----+------+------+
1 row in set (0.00 sec)

2、查询最后一行记录
select * from student order by id desc limit 1;
+----+------+------+
| id | name | age  |
+----+------+------+
| 10 | xie  |   20 |
+----+------+------+
1 row in set (0.00 sec)

3、查询前n行记录，如前5行
select * from student limit 5;
select * from student limit 0,5;
select * from student order by id asc limit 5;
上面三条语句的结果都是一样的，如下：
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | li   |   11 |
|  2 | zh   |   12 |
|  3 | chou |   13 |
|  4 | he   |   14 |
|  5 | lin  |   15 |
+----+------+------+
5 rows in set (0.00 sec)
	
4、查询后n行记录，如后5条，注意结果为倒序排序，因为用了desc
select * from student order by id desc limit 5;
+----+------+------+
| id | name | age  |
+----+------+------+
| 10 | xie  |   20 |
|  9 | wu   |   19 |
|  8 | yu   |   18 |
|  7 | chen |   17 |
|  6 | ll   |   16 |
+----+------+------+
5 rows in set (0.00 sec)

5、查询第m行到第n行记录，注意表中的记录下标是从0开始的，就像数组一样
select * from student limit m,n;  返回m+1到m+n行记录,m代表开始的下标，n代表查找的结果数，将返回n行结果
select * from student limit 2,8;  返回3到10行记录	
+----+------+------+
| id | name | age  |
+----+------+------+
|  3 | chou |   13 |
|  4 | he   |   14 |
|  5 | lin  |   15 |
|  6 | ll   |   16 |
|  7 | chen |   17 |
|  8 | yu   |   18 |
|  9 | wu   |   19 |
| 10 | xie  |   20 |
+----+------+------+
8 rows in set (0.00 sec)

select * from student limit 3,1; 返回第4行
+----+------+------+
| id | name | age  |
+----+------+------+
|  4 | he   |   14 |
+----+------+------+
1 row in set (0.00 sec)

6、查询一条记录($id)的下一条记录
select * from student where id>$id order by id asc limit 1;
如$id=4时将返回第5条记录
select * from student where id>4 order by id asc limit 1;
+----+------+------+
| id | name | age  |
+----+------+------+
|  5 | lin  |   15 |
+----+------+------+
1 row in set (0.00 sec)

7、查询一条记录($id)的上一条记录
select * from student where id<$id order by id desc limit 1;
如$id=4时将返回第3条记录
select * from student where id<4 order by id desc limit 1;
+----+------+------+
| id | name | age  |
+----+------+------+
|  3 | chou |   13 |
+----+------+------+
1 row in set (0.00 sec)