SQL Server 多表连接查询 关于日期DateAdd 和DateDiff
SELECT DATEADD(DAY,n-1,'20060101')AS orderdate,
O.orderid,o.custid,O.empid
FROM dbo.Nums
LEFT JOIN Sales.Orders AS O
ON DATEADD(DAY,n-1,'20060101')=O.orderdate
WHERE n<= DATEDIFF(DAY,'20060101','20081231')+1
ORDER BY orderdate
&
SELECT DATEADD(DAY,n-1,'20060101')AS orderdate,
O.orderid,o.custid,O.empid
FROM dbo.Nums
LEFT JOIN Sales.Orders AS O
ON n=DATEDIFF(DAY,o.orderdate,'20081231')
WHERE n<= DATEDIFF(DAY,'20060101','20081231')+1
ORDER BY orderdate
返回了两个不同的结果视图,这两种计算方法有什么不同