SQL实现如何计算项目进度总共天数情况、已经施工天数情况、以及施工进度百分比

SELECT DATEDIFF(DAY,e.StartDate,e.EndDate)as totaldays,
(SELECT COUNT(TaskID) from ConstructionManagement c  where
 c.Co_ProjectID=e.ProjectID) as aa,CAST(CAST((SELECT
COUNT(TaskID) from ConstructionManagement c  where
c.Co_ProjectID=e.ProjectID)AS
float)/CAST((DATEDIFF(DAY,e.StartDate,e.EndDate)) AS float)*100
 AS nvarchar(20))+'%' as yy ,e.* FROM EngineeringManagement e

解析：DATEDIFF-时间差函数方法（day(定义查询出来的内容为什么日期格式：这里可以是（year | quarter | month | week | day | hour | minute | second | millisecond）), e.StartDate,e.EndDate(2个参数，第一个定义开始日期，第二个定义结束日期))

totaldays：接收刚才查出来的天数

aa:接收查询出来已经进行过的天数

yy:接收计算出来的百分比

cast：数据库类型转换