求一句关于日期差的查询语句
2007-08-17   15:17:00   跟2007-08-17   15:17:30   差30秒,要怎么写啊 
------解决方案--------------------select datediff(second,  '2007-08-17 15:17:00 ',  '2007-08-17 15:17:30 ')
------解决方案--------------------select datediff(second, '2007-08-17 15:17:00 ', '2007-08-17 15:17:30 ')
------解决方案--------------------select datediff(ss, '2007-08-17 15:17:00 ', '2007-08-17 15:17:30 ')
------解决方案--------------------select datediff(second,  '2007-08-17 15:17:00 ',  '2007-08-17 15:17:30 ')   
 ......... 
 好快啊...LS的