Question

是否有人知道为什么在尝试为DATEPART（）或YEAR（）创建别名时可能会出错？

为了运行查询，我必须输入整个DATEPART（）函数（如果尝试使用YEAR（）则会出现相同的错误：

SELECT TOP 3 ShipCountry,DATEPART(year,orderdate), AvgFreight=AVG(freight)
FROM orders
WHERE DATEPART(year,orderdate)='2015' 
Group by ShipCountry, DATEPART(year,orderdate)
Order by AvgFreight desc

我试着这样做：

SELECT TOP 3 ShipCountry,OrdersByYear=DATEPART(year,orderdate), AvgFreight=AVG(freight)
FROM orders
WHERE OrdersByYear='2015' 
Group by ShipCountry, OrdersByYear
Order by AvgFreight desc

错误是：

消息207，级别16，状态1，行3无效的列名称＆＃39; OrdersByYear＆＃39;。消息207，级别16，状态1，行4无效的列名称＆＃39; OrdersByYear＆＃39;。

没有AVG别名的错误，谢谢！

Answer 1

别名很好。你不能在GROUP BY：

中使用别名

SELECT TOP 3 ShipCountry, DATEPART(year,orderdate) as orderyear,
       AVG(freight) as  AvgFreight
FROM orders
WHERE orderDate >= '2015-01-01' and orderDate < '2016-01-01'
Group by ShipCountry, DATEPART(year, orderdate)
Order by AvgFreight desc;

请注意，此查询的group by不需要它，因为您只查看一年：

select TOP 3 ShipCountry, max(datepart(year, orderdate)) as orderyear,
       AVG(freight) as  AvgFreight
from orders
where orderDate >= '2015-01-01' and orderDate < '2016-01-01'
Group by ShipCountry
Order by AvgFreight desc;

请注意，我更改了where子句中的日期比较。这使优化器更容易生成更好的查询计划。

SQL错误为DATEPART（）或YEAR（）创建别名

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