如何从别名列中获取数据

Question

我正在尝试根据别名列进行计算。

SELECT 
    Aged, NotAged, Aging
FROM
    (SELECT 
         DATEDIFF(DAY, CASE WHEN Stat = 'HOLD' THEN Created ELSE Opened END,
                      CASE WHEN Stat = 'Closed' THEN Closed ELSE GETDATE() END) AS Aged,
         DATEDIFF(DAY, CASE WHEN Aged <= 25 THEN GETDATE() AS NotAged ELSE GETDATE() END) AS Aging
     FROM 
         DM.Claim 
     INNER JOIN
         DM.LDesc ON LDescKey = LDescKey) data

如何根据别名列进行计算以获取NotAged和Aging ？

预期输出将是 Ageed {1 2 35} NotAged {1 2} Aging {35}

Answer 1

如果没有样本数据和预期结果，很难确定您想要什么（聚合？），但您可以使用CROSS APPLY (VALUES来创建计算列，您甚至可以通过引用前一个列来链接它们。例如。

SELECT 
    v1.Aged,
    v1.NotAged,
    v2.Aging
FROM
    DM.Claim AS c
INNER JOIN
    DM.LDesc AS ld ON ld.LDescKey = c.LDescKey
CROSS APPLY (VALUES (
    DATEDIFF(DAY, CASE WHEN Stat = 'HOLD' THEN Created ELSE Opened END,
                  CASE WHEN Stat = 'Closed' THEN Closed ELSE GETDATE() END,
    CASE WHEN Aged <= 25 THEN GETDATE() END
) ) AS v1(Aged, NotAged)
CROSS APPLY (VALUES (
    DATEDIFF(DAY, v1.NotAged ELSE GETDATE() END, v1.Aged)
) ) AS v2(Aging);

Answer 2

Charlieface 建议使用 CROSS APPLY 就可以了。
另一种选择是使用 CTE（公用表表达式），因此计算（和别名）列可以在下游表达式中使用。 这是一个包含一些虚构数据的示例。

with somedata as (
    SELECT
        *
    FROM ( values
        ('HOLD', '2022-06-01', '2022-06-02', '2022-07-15'),
        ('HOLD', '2022-07-01', '2022-07-02', '2022-07-15'),
        ('Closed', '2022-06-01', '2022-06-02', '2022-07-15'),
        ('Closed', '2022-07-01', '2022-07-02', '2022-07-15')
    ) vals (Stat, Created, Opened, Closed)
)
,
precalc as (
    select
        *,
        Aged = DATEDIFF(
            DAY,
            CASE WHEN Stat = 'HOLD' THEN Created ELSE Opened END,
            CASE WHEN Stat = 'Closed' THEN Closed ELSE GETDATE() END
        )
    from somedata
)
SELECT 
    Aged,
    NotAged = case when Aged <25 then Aged end,
    Aging = case when Aged >=25 then Aged end,
    *
FROM precalc

输出 (20220721)

陈年	未老化	老化	统计	已创建	打开	关闭	陈年
50	无效的	50	抓住	44713	44714	44757	50
20	20	无效的	抓住	44743	44744	44757	20
43	无效的	43	关闭	44713	44714	44757	43
13	13	无效的	关闭	44743	44744	44757	13