如何在SQL中获取两个日期之间的差异

我想知道如何在两个日期之间取得差异，这里

date1 =用户首次注册或在（注册）表格中表示最高值，日期2 =当前日期。

我们知道的第一个日期很简单，但是如果我们不知道第一个注册用户日期那么我们如何得到它？

我有一个表注册列（ID ，reg_date）我想知道reg_date（第一个注册用户日期）和计算机当前日期之间的日期差异。









提前付款



我的尝试：



SELECT DATEDIFF（day，'2016-06-20'， GETDATE（））AS DiffDate

差值为37.我们很容易得到，因为我们知道登记表中前1个日期是'2016-06-20'。

I want to know how to get difference between two date,here
date1=first registration of user or say top value in table in (registration) table and date2=current date.
Its simple to get is we know first date, but suppose if we don't know about first registered user date then how we get It?
I have a table registration column (ID,reg_date) I want to know date difference between reg_date (first registered user date) and current date of computer.




thanks in advance

What I have tried:

SELECT DATEDIFF(day,'2016-06-20',GETDATE()) AS DiffDate
difference is 37. we get easily because we know top 1 date is '2016-06-20' in registration table.