MySQL SUBSTRING() 函数

从字符串中提取子字符串（从位置 5 开始，提取 3 个字符）：

SELECT SUBSTRING("SQL Tutorial", 5, 3) AS ExtractString;

定义和用法

SUBSTRING() 函数从字符串中提取子字符串（从任意位置开始）。

笔记：这个SUBSTR()和中（）函数等于 SUBSTRING() 函数。

SUBSTRING( string, start, length)

或者：

SUBSTRING( string FROM start FOR length)

Parameter	Description
string	Required. The string to extract from
start	Required. The start position. Can be both a positive or negative number. If it is a positive number, this function extracts from the beginning of the string. If it is a negative number, this function extracts from the end of the string
length	Optional. The number of characters to extract. If omitted, the whole string will be returned (from the start position)

工作于：	从 MySQL 4.0 开始