ＳＱＬ ＳＥＲＶＥＲ －－ＳＴＵＤＹ（12）

UNIQUE 用法：

 

http://webdesign.enjoyitsimply.com/sql/sql_unique

 

CHECK用法：

 

http://webdesign.enjoyitsimply.com/sql/sql_check

 

SQL datetime的大小比较~~

http://blog.gisforum.net/u/28376/archives/2007/314.html

SELECT hiredate
FROM employees
WHERE datediff(day,cast('1993-05-03' as datetime),hiredate) >0