日期函数

-----------------------------输出所有数据中通话时长最长的5条记录-------------------------------------
select
top 5 --前五
*,
通话时长 = datediff(second,StartDateTime,EndDateTime)
from CallRecords
order by 通话时长 desc


-----------------------------输出所有数据中拨打长途号码（以0开头）的总时长--------------------------
select
总时长 = sum(datediff(second,StartDateTime,EndDateTime))
from CallRecords
where TelNum like '0%'

-------------------------------输出本月通话时间前三的电话编号------------------------------------------
select
top 3
电话编号 = CallerNumber,
通话时长 = datediff(second,StartDateTime,EndDateTime)
from CallRecords
where datediff(second,StartDateTime,EndDateTime) = 0 --表示是本月
group by CallerNumber
order by 通话时长 desc

---------------------------------输出本月拨打电话次数最多的三个电话编号----------------------------------
select
top 3
电话编号 = CallerNumber,
电话次数 = count (*)
from CallRecords
where datediff(second,StartDateTime,EndDateTime) = 0
group by 电话编号
order by 电话次数