Question

我有以下查询：

SELECT EMAIL.MAILADDRESS, COUNT (DISTINCT CUSTOMER.CUSTOMER_ID) distinct_count
    FROM    (  SELECT CUSTOMER_ID,
                      TRUNC (MAX (UPDATE_DATE)) AS UPDATE_TARIHI,
                      TRUNC (MIN (INSERT_DATE)) AS DATA_ENTRY_DATE,
                      'YES' AS MAILADDRESS
                 FROM ELECTRONIC_ADDRESS
                WHERE ADDRESS_TYPE = 'ELECTRONIC'
             GROUP BY CUSTOMER_ID) EMAIL
         RIGHT OUTER JOIN
            CUSTOMER
         ON (EMAIL.CUSTOMER_ID = CUSTOMER.CUSTOMER_ID)
GROUP BY EMAIL.MAILADDRESS

我正在加入电子邮件（subquery-incoludes'E'AS MAILADDRESS）和客户表。有些客户没有电子邮件地址，所以我认为结果应该像下面的条款：

MAILADDRESS        DISTINCT_COUNT
YES                      158945
NULL                      76345

但是当我运行此查询时，只显示第一行（其邮件地址为YES）

如果我将EMAIL.MAILADDRESS子句更改为所选列中的nvl（EMAIL.MAILADDRESS，'NO'）并按部分分组，则查询将完美运行。但我无法解决问题，因为该查询是从Business Objects Universe生成的，所以无法更改查询。

我们正在写这部分：

   SELECT CUSTOMER_ID,
                  TRUNC (MAX (UPDATE_DATE)) AS UPDATE_TARIHI,
                  TRUNC (MIN (INSERT_DATE)) AS DATA_ENTRY_DATE,
                  'YES' AS MAILADDRESS
             FROM ELECTRONIC_ADDRESS
            WHERE ADDRESS_TYPE = 'ELECTRONIC'
         GROUP BY CUSTOMER_ID

然后在此部分和客户表之间构建一个正确的连接关系。

我该如何解决这个问题？为什么Oracle没有显示空值？

Answer 1

使用以下SQL，我无法重新创建您的问题。

CREATE TABLE a1 (a NUMBER);

CREATE TABLE a2 (a NUMBER);

INSERT INTO a1
   SELECT     LEVEL
   FROM       DUAL
   CONNECT BY LEVEL <= 10;

INSERT INTO a2
   SELECT     LEVEL
   FROM       DUAL
   CONNECT BY LEVEL <= 20;

SELECT   a1.a, COUNT(DISTINCT a2.a)
FROM     a1 RIGHT OUTER JOIN a2 ON a1.a = a2.a
GROUP BY a1.a;

这表明问题出在数据中，而不是SQL中。是否有可能当客户没有电子邮件地址时，ELECTRONIC_ADDRESS表中仍有记录，但其他一些列为空？

如果是这种情况，我会按如下方式更改您的子查询（其中“地址”是包含电子邮件地址的实际列）：

   SELECT CUSTOMER_ID,
          TRUNC (MAX (UPDATE_DATE)) AS UPDATE_TARIHI,
          TRUNC (MIN (INSERT_DATE)) AS DATA_ENTRY_DATE,
          CASE WHEN ADDRESS IS NULL 
               THEN NULL 
               ELSE 'YES' 
               END AS MAILADDRESS
     FROM ELECTRONIC_ADDRESS
    WHERE ADDRESS_TYPE = 'ELECTRONIC'
 GROUP BY CUSTOMER_ID

Answer 2

您说加入此查询

 select customer_id
       ,trunc(max(update_date)) as update_tarihi
       ,trunc(min(insert_date)) as data_entry_date
       ,'YES' as mailaddress
   from electronic_address
  where address_type = 'ELECTRONIC'
  group by customer_id

到客户表。这是否意味着您只会获得具有电子邮件地址的记录（='YES'）？

oracle null值问题与group by

2 个答案: