如果表字段的类型为varchar型，但是里面存储的是纯数字，怎么实现按照数字的大小来排序？
下面的方法对于mysql和oracle都实用
order by 字段+0
order by 字段*1
等等都可以实现

mysql> create table tn (id varchar(30),name varchar(50));
mysql> show create table tn;
+-------+-----------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table|
+-------+-----------------------------------------------------------------------------------------------------------------------------+
| tn| CREATE TABLE `tn` (
`id` varchar(30) DEFAULT NULL,
`name` varchar(50) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |


mysql> insert into tn values (1,'a');
Query OK, 1 row affected (0.01 sec)


mysql> insert into tn values (10,'b');
Query OK, 1 row affected (0.00 sec)


mysql> insert into tn values (11,'bb');
Query OK, 1 row affected (0.00 sec)


mysql> insert into tn values (2,'bb');
Query OK, 1 row affected (0.00 sec)


mysql> insert into tn values (5,'c');
Query OK, 1 row affected (0.00 sec)


mysql> insert into tn values (3,'f');
Query OK, 1 row affected (0.00 sec)


mysql> insert into tn values (6,'g');
Query OK, 1 row affected (0.00 sec)


mysql> select * from tn;

+------+------+
| id| name |
+------+------+
| 1| a|
| 10| b|
| 11| bb|
| 2| bb|
| 5| c|
| 3| f|
| 6| g|
+------+------+

使用order by语句进行排序
mysql> select * from tn order by id desc;
+------+------+
| id| name |
+------+------+
| 6| g|
| 5| c|
| 3| f|
| 2| bb|
| 11| bb|
| 10| b|
| 1| a|
+------+------+
7 rows in set (0.00 sec)

貌似是不起作用，因为id列的值存的是字符串类型的
解决：
使用字段+0解决

mysql> select * from tn order by id+0 desc;
+------+------+
| id| name |
+------+------+
| 11| bb|
| 10| b|
| 6| g|
| 5| c|
| 3| f|
| 2| bb|
| 1| a|
+------+------+
7 rows in set (0.00 sec)

或者使用 字段*1解决
mysql> select * from tn order by id*1 desc;
+------+------+
| id| name |
+------+------+
| 11| bb|
| 10| b|
| 6| g|
| 5| c|
| 3| f|
| 2| bb|
| 1| a|
+------+------+
7 rows in set (0.00 sec)