关于日期统计的SQL语句怎么写？

Question

select datediff(mi,beginacst,endacst) *rent from tablename where.....

Answer 1

select datediff(day,beginDate,endDate) as 天数,..
from tbl
....

Answer 2

select datediff(dd,beginDate,endDate) * rent as aa from tablename

Answer 3

select @a=rent*diffdate(day,begindate,enddate) from table 
print(@a)

Answer 4

不好意思，写错
select @a=rent*datediff(day,begindate,enddate) from table 
print(@a)