2

我有一个表 billing_history 包含以下字段

CREATE TABLE [dbo].[BILLING_HISTORY2](
[ID] [int] IDENTITY(1,1) NOT NULL,
[READING_MONTH_YEAR] [date] NULL,
[READING] [int] NULL,
[CONSUMER_ID] [int] NULL,
[payment_status] [bit] NOT NULL
)

http://www.sqlfiddle.com/#!3/892e0/5

以下查询返回消费者的 MAX Paid 和 Max Unpaid Values

SELECT MAX(READING) AS 'MAXIMUM_PAID_READING',consumer_id from billing_history2
where payment_status=0 GROUP BY consumer_id;

SELECT MAX(READING) AS 'MAXIMUM_UNPAID_READING',consumer_id from billing_history2
where payment_status=1 GROUP BY consumer_id;

但是，当我加入它们以从 MAXIMUM_UNPAID_READING 中减去 MAXIMUM_PAID_READING 以获得当前读数时，通过加入上述两个查询，它会导致返回所有具有匹配 consumer_id 的记录。因此，如果消费者尚未支付任何账单，则 ID 将在 PAID_READING 中省略，因此 INNER JOIN 不会返回任何结果。如果我使用 FULL OUTER JOIN，它会返回所有记录，但将差异设置为 NULL。

我需要通过从以前的未付 USAGE 中减去客户的当前 USAGE 来找出它。

我如何以这样一种方式加入这两个查询，以便无论该人过去是否支付过帐单，都可以找到结果差异。

4

3 回答 3

1

不要加入他们。

SELECT
    MAX(CASE WHEN payment_status=0 THEN READING ELSE NULL END) AS 'MAXIMUM_PAID_READING',
    MAX(CASE WHEN payment_status=1 THEN READING ELSE NULL END) AS 'MAXIMUM_UNPAID_READING',

    MAX(CASE WHEN payment_status=0 THEN READING ELSE NULL END)
     - MAX(CASE WHEN payment_status=1 THEN READING ELSE NULL END)
        AS 'DIFF_READING',

    consumer_id from billing_history2
GROUP BY consumer_id;

如果要处理来自 MAX 函数的 NULL 值，请使用 ISNULL 函数：

SELECT
    ISNULL(MAX(CASE WHEN payment_status=0 THEN READING ELSE NULL END),0) AS 'MAXIMUM_PAID_READING',
    ISNULL(MAX(CASE WHEN payment_status=1 THEN READING ELSE NULL END),0) AS 'MAXIMUM_UNPAID_READING',

    ISNULL(MAX(CASE WHEN payment_status=0 THEN READING ELSE NULL END),0)
     - ISNULL(MAX(CASE WHEN payment_status=1 THEN READING ELSE NULL END),0)
        AS 'DIFF_READING',

    consumer_id from billing_history2
GROUP BY consumer_id;
于 2013-02-18T07:46:16.077 回答
0

可以使用左外连接，但在最大值上使用 isnull 。

前任：

max(...) - isnull(max(...),0) as ...
于 2013-02-18T07:48:47.987 回答
0

在您的情况下，有必要使用CASE表达式

SELECT CONSUMER_ID,
       MAX(CASE WHEN payment_status = 0 THEN READING ELSE 0 END) AS 'MAXIMUM_PAID_READING',
       MAX(CASE WHEN payment_status = 1 THEN READING ELSE 0 END) AS 'MAXIMUM_UNPAID_READING', 
       MAX(CASE WHEN payment_status = 0 THEN READING ELSE 0 END) - 
       MAX(CASE WHEN payment_status = 1 THEN READING ELSE 0 END) AS diff
FROM billing_history2
GROUP BY consumer_id

SQLFiddle上的演示

于 2013-02-18T07:50:37.773 回答