第17课:字符串操作

1.从左开始截取字符串 
left(str, length) 
说明:left(被截取字段,截取长度) 
例:select left(content,200) as c from godeye

2.从右开始截取字符串 
right(str, length) 
说明:right(被截取字段,截取长度) 
例:select right(content,200) as c from godeye

3.截取字符串
substring(str, pos)
substring(str, pos, length) 
说明:substring(被截取字段,从第几位开始截取) 
substring(被截取字段,从第几位开始截取,截取长度) 
例:select substring(content,5) as c from godeye
select substring(content,5,200) as c from godeye 
(注:如果位数是负数 如-5 则是从后倒数位数,到字符串结束或截取的长度)

4.按关键字截取字符串 
substring_index(str,delim,count) 
说明:substring_index(被截取字段,关键字,关键字出现的次数) 
例:select substring_index("123|godeye.org","|",-1) as c from godeye 
结果:godeye.org
(注:如果关键字出现的次数是负数 如-2 则是从后倒数,到字符串结束)