求一句关于日期差的查询语句解决思路

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 ')

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好快啊...LS的