CAST 和 CONVERT
将某种数据类型的表达式显式转换为另一种数据类型。CAST 和 CONVERT 提供相似的功能。

语法
使用 CAST：

CAST ( expression AS data_type )

使用 CONVERT：

CONVERT (data_type[(length)], expression [, style])
1。2222222222转换为16位的84746B8E,取后面6位746B8E，然后再转换为
7629710
select 22222222-convert(bigint,2222222222/convert(int,0x1000000)*
convert(int,0x1000000)

2。SELECT SUBSTRING(title, 1, 30) AS Title, ytd_sales
FROM titles
WHERE CAST(ytd_sales AS char(20)) LIKE ''''3%''''
3.显示时加百分号
select cast(field1/field2 as varchar(20))+''''%''''

4.SELECT CAST(ROUND(ytd_sales/price, 0) AS int) AS ''''Copies''''
FROM titles

5.select convert(type,case .......when....end)

6>密码有大小写的比较
select *
from tablename
where cast(ma as varbinary)=cast(:para as varbinary)

7.日期转换
select convert(char(10),getdate(),101) //102,121
101 04/18/2003
102 2003.04.18
121 2003-04-18