Question

我使用以下查询来尝试通过减去两列之间的值来获取日期差异。以下是此查询的一部分：

SELECT
ISNULL(MIN(c.CreatedOn), 0) AS [StartDate], 
ISNULL(MIN(s.CreatedOn), 0) AS [EndDate],
Duration = [EndDate]-[StartDate]
FROM MyTable
INNER JOIN...

我收到的错误表明我的列名无效。是否有可能以这种方式编写查询？

Answer 1

以前定义的列别名不能在同一查询中使用。改为使用实际计算。

SELECT
ISNULL(MIN(c.CreatedOn), 0) AS [StartDate], 
ISNULL(MIN(s.CreatedOn), 0) AS [EndDate],
Duration = ISNULL(MIN(s.CreatedOn), 0)-ISNULL(MIN(c.CreatedOn), 0)
FROM MyTable
INNER JOIN...

Answer 2

您不能在同一查询中使用别名。如果必须使用它们，则可以使用嵌套查询或WITH语句。

嵌套查询

Select StartDate, EndDate,
       Duration = [EndDate]-[StartDate]
From
(
    SELECT
    ISNULL(MIN(c.CreatedOn), 0) AS [StartDate], 
    ISNULL(MIN(s.CreatedOn), 0) AS [EndDate]
    FROM MyTable
    INNER JOIN...
) InnerQuery

WITH声明

;With InnerQuery AS
(
    SELECT
    ISNULL(MIN(c.CreatedOn), 0) AS [StartDate], 
    ISNULL(MIN(s.CreatedOn), 0) AS [EndDate]
    FROM MyTable
    INNER JOIN...
) 
Select StartDate, EndDate,
       Duration = [EndDate]-[StartDate]
From InnerQuery

Answer 3

有一个datediff function

select datediff(day, min('12/01/2014'), min(getdate()))

P.S。，当您将日期数据类型添加到int时，您还期待什么？

select isnull(cast(null as date), 0)

在SQL中减去列时出错

3 个答案: