SQL MID() 使用实例教程

mid（）函数
mid（）函数是用来提取字符的文本字段。

数据库mid（）语法

SELECT MID(column_name,start[,length]) FROM table_name

Parameter Description
column_name Required. The field to extract characters from.
start Required. Specifies the starting position (starts at 1).
length Optional. The number of characters to return. If omitted, the MID() function returns the rest of the text.

Parameter	Description
column_name	Required. The field to extract characters from.
start	Required. Specifies the starting position (starts at 1).
length	Optional. The number of characters to return. If omitted, the MID() function returns the rest of the text.

来看个实例吧.

  LastName FirstName Address City
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

	LastName	FirstName	Address	City
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes
3	Pettersen	Kari	Storgt 20	Stavanger

现在，我们要提取的前四个字符的“城市”专栏以上。 

我们使用下面的SELECT语句：
SELECT MID(City,1,4) as SmallCity FROM Persons
结果.
SmallCity
Sand
Sand
Stav

SmallCity
Sand
Sand
Stav

补充：数据库,mysql教程