1、大小写转换：UPPER(exp)、LOWER(exp)
SELECT UPPER('abc')
> ABC
SELECT LOWER('AbC')
> abc
2、字符串查找：CHARINDEX( exp_find , exp_src [ , start_location ] )
SELECT CHARINDEX('de','abcdefghijklmn')
> 4
//exp_src索引下标从1开始，找不到则返回0
3、字符串截取：SUBSTRING ( exp, start, length )
SELECT SUBSTRING('abcdefghijklmn',4,3)
> def
4、类型转换：CAST(exp AS data_type)
SELECT CAST('1988/02/15' AS DATETIME)
> 1988-02-15 00:00:00.000
5、取字符串长度：LEN(exp)
SELECT LEN('abcdefgh')
> 8
