接收 DB2 中列 SUM 的不同输出

Posted 2023-03-22

【中文标题】接收 DB2 中列 SUM 的不同输出

【英文标题】：Receiving different output for column SUMs in DB2

【发布时间】：2021-08-12 09:18:28

【问题描述】：

我在 DB2 中有下表：

COLUMN_NAME	DATA_TYPE	TYPE_NAME	COLUMN_SIZE	COLUMN_TEXT
DMPROD	-2	CHAR () FOR BIT DATA	35	Product Code
DMPTYP	-2	CHAR () FOR BIT DATA	1	Period Type
DMTYPE	-2	CHAR () FOR BIT DATA	6	Type of Data
DMVL01	3	DECIMAL	17	Value Period 1
DMVL02	3	DECIMAL	17	Value Period 2
DMVL03	3	DECIMAL	17	Value Period 3
DMVL04	3	DECIMAL	17	Value Period 4
DMVL05	3	DECIMAL	17	Value Period 5
DMVL06	3	DECIMAL	17	Value Period 6
DMVL07	3	DECIMAL	17	Value Period 7
DMVL08	3	DECIMAL	17	Value Period 8
DMVL09	3	DECIMAL	17	Value Period 9
DMVL10	3	DECIMAL	17	Value Period 10
DMVL11	3	DECIMAL	17	Value Period 11
DMVL12	3	DECIMAL	17	Value Period 12
DMYEAR	3	DECIMAL	4	Fiscal Year

下面的查询将返回每个周期类型的价值周期总和，并将它们分组到产品代码中

SELECT
    D.DMPROD,
    Sum(D.DMVL01 + D.DMVL02 + D.DMVL03 + D.DMVL04 + D.DMVL05 + D.DMVL06) AS Total
FROM
        DWM D
WHERE
        D.DMYEAR IN (2022)
    AND D.DMPTYP = 'M'
    AND D.DMTYPE IN ('RTNQTY','SLSQTY')
GROUP BY
        D.DMPROD
ORDER BY
    1;

初始输出：

DMPROD	TOTAL
11105	1145.75000
11350	625.37400
13135	2270.50000
13282	-0.27500
13344	-1.03300
15105	784

然后，由于其他成员的反馈，我将其更改为使用子查询。这是首选格式：

SELECT
    D.DMPROD,
    (SLSQTY + RTNQTY) AS Total
FROM
    (
    SELECT
        D.DMPROD,
        Sum(CASE WHEN D.DMTYPE = 'RTNQTY' THEN Total END) AS RTNQTY,
        Sum(CASE WHEN D.DMTYPE = 'SLSQTY' THEN Total END) AS SLSQTY
    FROM
        (
        SELECT
            D.*,
            (D.DMVL01 + D.DMVL02 + D.DMVL03 + D.DMVL04 + D.DMVL05 + D.DMVL06) AS Total
        FROM
            DWM AS D
    ) AS D
    WHERE
        D.DMYEAR IN (2022)
        AND D.DMPTYP = 'M'
    GROUP BY
        D.DMPROD
) AS D
ORDER BY 1;

但请注意总和不一样（初始输出是正确的）：

DMPROD	TOTAL
11105	1145.75000
11350	625.37400
13135	2270.50000
13282
13344
15105

我在哪里犯了错误？

【问题讨论】：

很可能 SLSQTY 或 RTNQTY 为 null ，试试coalesce(SLSQTY, 0) + coalesce(RTNQTY, 0)

【参考方案1】：

这些表达方式：

    Sum(CASE WHEN D.DMTYPE = 'RTNQTY' THEN Total END) AS RTNQTY,
    Sum(CASE WHEN D.DMTYPE = 'SLSQTY' THEN Total END) AS SLSQTY

如果结果中没有DMTYPE 的行，则可以返回NULL。这反过来又会影响这个计算：

(SLSQTY + RTNQTY) AS Total

最简单的解决方案是添加ELSE 0:

    Sum(CASE WHEN D.DMTYPE = 'RTNQTY' THEN Total ELSE 0 END) AS RTNQTY,
    Sum(CASE WHEN D.DMTYPE = 'SLSQTY' THEN Total ELSE 0 END) AS SLSQTY

这样就避免了NULL的值，所以总的计算不会变成NULL。

【讨论】：

我认为它可能是 NULL，谢谢，确认这个作品

【参考方案2】：

可能存在某些DMPROD 组不包含带有某些DMTYPE 的行的情况。此类型的 SUM 为 NULL，如果在 + 运算符中使用此类值，则结果为 NULL。 您可以按原样检查以下示例：

SELECT
  DMPROD
, RTNQTY
, SLSQTY
, RTNQTY + SLSQTY AS TOTAL_new 
, TOTAL_orig
, COALESCE (RTNQTY, 0) + COALESCE (SLSQTY, 0) AS TOTAL_mustbe 
FROM
(
SELECT
  DMPROD
, SUM (CASE WHEN DMTYPE = 'RTNQTY' THEN Total END) AS RTNQTY
, SUM (CASE WHEN DMTYPE = 'SLSQTY' THEN Total END) AS SLSQTY
, SUM (Total) AS TOTAL_orig
FROM 
(
VALUES
  (1, 'RTNQTY', 1)
, (1, 'SLSQTY', 1)
, (2, 'RTNQTY', 1)
) MY_TAB (DMPROD, DMTYPE, Total)
GROUP BY DMPROD
);

结果是：

DMPROD	RTNQTY	SLSQTY	TOTAL_NEW	TOTAL_ORIG	TOTAL_MUSTBE
1	1	1	2	2	2
2	1			1	1