关于mysql的小问题

feetable为费用表，fee为费用 beginDate为开始时间，endDate为结束时间
select sum(fee*?) from feetable
？为：endDate-beginDate的值，如果大于12就取12，小于12就取他们之间的差值~！
在sql语句中能否做判断？ 

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帮顶~

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select sum(fee*(case when endDate-beginDate >= 12 then 12 else endDate-beginDate end)) from feetable

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mysql?日期差用datediff
select sum(fee*(if(datediff(endDate,beginDate)>=0,12, endDate-beginDate ))) from table

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SQL code:
select sum(fee*LEAST(datediff(endDate,beginDate),12)) from feetable

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或者

SQL code:
select sum(fee*(if(datediff(endDate,beginDate)>=12,12, datediff(endDate,beginDate) ))) from feetable