ORA-00979: 不是 GROUP BY 表达式（Case 语句问题）答案

【问题标题】：ORA-00979: not a GROUP BY expression (Case statement issue)ORA-00979: 不是 GROUP BY 表达式（Case 语句问题）
【发布时间】：2017-06-20 06:30:04
【问题描述】：

我在以下查询中收到 ORA-00979 错误消息。我应该先声明我已经阅读了 Stack Overflow 上关于此错误的许多讨论，但仍然找不到解决方案。我也确信错误来自 CASE 语句，因为当我完全删除该语句时，查询已产生结果，并且当我删除除“SUM(Z.EQUITY_FOUR)”之外的所有 CASE 语句时，我也收到了结果（也就是说，我也确信 EQUITY_FOUR 从中提取的数据库没有问题）。

SELECT 
EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE) as Yr,
EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE) as Mth,
Q.CITY as City,
CASE WHEN pp.ISACTIVE = 'NO' 
AND EXTRACT(YEAR FROM HDS.CANCELLATION_DATE) = EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE) 
AND EXTRACT(MONTH FROM HDS.CANCELLATION_DATE) = EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE)
THEN SUM(Z.EQUITY_FOUR)
END as Cancelled

(From Statement)

(Where Statement)

GROUP BY EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE),
     EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE),
     Q.CITY,
     CASE 
     WHEN pp.ISACTIVE = 'NO' 
     AND EXTRACT(YEAR FROM HDS.CANCELLATION_DATE) = EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE) 
     AND EXTRACT(MONTH FROM HDS.CANCELLATION_DATE) = EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE)
     THEN SUM(Z.EQUITY_FOUR)
     END

关于 Group BY 子句中的 CASE 语句，在进行研究时，我阅读了这篇 (ORA-00979: not a GROUP BY expression issue) 帖子，其中包含两个回复，说明将完整的 CASE 语句添加到 GROUP BY 表达式中，并且该帖子的作者声称为他的查询工作。但是，我仍然收到上述错误。

感谢您的帮助！

【问题讨论】：

标签： oracle case aggregate-functions

【解决方案1】：

我想你想要SUM() 中的CASE：

SELECT EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE) as Yr,
       EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE) as Mth,
       Q.CITY as City,
       SUM(CASE WHEN pp.ISACTIVE = 'NO' AND
                     EXTRACT(YEAR FROM HDS.CANCELLATION_DATE) = EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE) AND
                     EXTRACT(MONTH FROM HDS.CANCELLATION_DATE) = EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE)
                THEN Z.EQUITY_FOUR
           END) as Cancelled
(From Statement)
(Where Statement)
GROUP BY EXTRACT(YEAR FROM HDS.MORTGAGE_START_DATE),
         EXTRACT(MONTH FROM HDS.MORTGAGE_START_DATE),
         Q.CITY;

【讨论】：