关于group by - Oracle 10g

Question

使用Oracle10g。我在GROUP BY子句中使用“case when”。问题是当我使用：

a.book_name IN (SELECT BOOK 
        FROM BOOK_CONF) 

这是说它不是一个GROUP BY子句。有谁能帮我解决这个问题吗？

SELECT pub_name, 
     CASE 
      WHEN a.book_name IN (SELECT BOOK FROM BOOK_CONF) THEN 'UNI' 
      WHEN a.book_name ='JAVA' THEN 'JAVA'  
      ELSE 'MIS'  
     END) test, 
     COUNT(*) 
    FROM books a 
GROUP BY pub_name, 
     CASE 
      WHEN a.book_name in (SELECT BOOK FROM BOOK_CONF) THEN 'UNI' 
      WHEN a.book_name ='JAVA' THEN 'JAVA'  
     ELSE 'MIS' 

Answer 1

最早的Oracle允许引用列别名是ORDER BY - 你会得到ORA-00904：否则无效标识符（IME即高达并包含10g - 如果在11g中改变，则不知道）。因此，为了适应最简单的方法是使用派生表/内嵌视图：

SELECT x.pub_name, 
     x.test, 
     COUNT(*) 
    FROM (SELECT a.pub_name, 
       CASE 
        WHEN a.book_name IN (SELECT BOOK FROM BOOK_CONF) THEN 'UNI' 
        WHEN a.book_name ='JAVA' THEN 'JAVA'  
        ELSE 'MIS'  
       END AS test 
      FROM BOOKS a) x 
GROUP BY x.pub_name, x.test 

Answer 2

select pub_name, 
(CASE WHEN a.book_name in(SELECT BOOK FROM BOOK_CONF) THEN 'UNI' 
WHEN a.book_name ='JAVA' THEN 'JAVA' ELSE 'MIS' END) AS test, 
count(*) from books a group by pub_name, test; 

我相信你没有包含在GROUP BY子句中的测试。让我知道是否可行

Answer 3

由于a.book_name是什么你对案件的内部测试，这是你应该有一群什么：

select a.pub_name, (CASE WHEN a.book_name in (SELECT BOOK FROM BOOK_CONF) THEN 'UNI' 
         WHEN a.book_name ='JAVA' THEN 'JAVA'  
         ELSE 'MIS'  
        END) test, count(*) 
from books a 
group by a.pub_name, a.book_name 

Answer 4

请允许我总结一下，因为有一些好的，这里的一些不好的建议混合在一起。

首先你的表格有一些样本数据：

SQL> create table books (book_name,pub_name) 
    2 as 
    3 select 'JAVA', 'PUB1' from dual union all 
    4 select 'JAVA', 'PUB2' from dual union all 
    5 select 'ABC', 'PUB1' from dual union all 
    6 select 'XYZ', 'PUB3' from dual union all 
    7 select 'KLM', 'PUB3' from dual 
    8/

Table created. 

SQL> create table book_conf (book) 
    2 as 
    3 select 'XYZ' from dual union all 
    4 select 'KLM' from dual 
    5/

Table created. 

您的疑问：

SQL> SELECT pub_name 
    2  , CASE 
    3   WHEN a.book_name IN (SELECT BOOK FROM BOOK_CONF) THEN 
    4   'UNI' 
    5   WHEN a.book_name ='JAVA' THEN 
    6   'JAVA' 
    7   ELSE 
    8   'MIS' 
    9   END test 
10  , COUNT(*) 
11 FROM books a 
12 GROUP BY pub_name 
13  , CASE 
14   WHEN a.book_name in (SELECT BOOK FROM BOOK_CONF) THEN 
15   'UNI' 
16   WHEN a.book_name ='JAVA' THEN 
17   'JAVA' 
18   ELSE 
19   'MIS' 
20   END 
21/
     WHEN a.book_name IN (SELECT BOOK FROM BOOK_CONF) THEN 
      * 
ERROR at line 3: 
ORA-00979: not a GROUP BY expression 

这并不是因为CASE表达式是不是group by子句允许的。这是因为您在GROUP BY子句中使用了SELECT语句。如果换成“IN（SELECT本书从book_conf）”改为“IN（‘XYZ’，‘荷航’）”，你会看到你的语句现在成功：

SQL> SELECT pub_name 
    2  , CASE 
    3   WHEN a.book_name IN ('XYZ','KLM') THEN 
    4   'UNI' 
    5   WHEN a.book_name ='JAVA' THEN 
    6   'JAVA' 
    7   ELSE 
    8   'MIS' 
    9   END test 
10  , COUNT(*) 
11 FROM books a 
12 GROUP BY pub_name 
13  , CASE 
14   WHEN a.book_name in ('XYZ','KLM') THEN 
15   'UNI' 
16   WHEN a.book_name ='JAVA' THEN 
17   'JAVA' 
18   ELSE 
19   'MIS' 
20   END 
21/

PUB_ TEST COUNT(*) 
---- ---- ---------- 
PUB1 MIS   1 
PUB1 JAVA   1 
PUB2 JAVA   1 
PUB3 UNI   2 

4 rows selected. 

下面的查询看起来不错，不会产生一个错误，但给出了不同的结果，因为你现在BOOK_NAME分组的CASE表达式来代替：

SQL> select a.pub_name 
    2  , (CASE WHEN a.book_name in (SELECT BOOK FROM BOOK_CONF) THEN 'UNI' 
    3    WHEN a.book_name ='JAVA' THEN 'JAVA' 
    4    ELSE 'MIS' 
    5   END) test 
    6  , count(*) 
    7 from books a 
    8 group by a.pub_name 
    9  , a.book_name 
10/

PUB_ TEST COUNT(*) 
---- ---- ---------- 
PUB1 MIS   1 
PUB1 JAVA   1 
PUB2 JAVA   1 
PUB3 UNI   1 
PUB3 UNI   1 

5 rows selected. 

OMG小马在内嵌视图通过表达封装组使用正确的方法：

SQL> select pub_name 
    2  , book_type 
    3  , count(*) 
    4 from (select pub_name 
    5    , case 
    6     when book_name in (select book from book_conf) then 
    7     'UNI' 
    8     when book_name = 'JAVA' then 
    9     'JAVA' 
10     else 
11     'MIS' 
12     end book_type 
13    from books 
14  ) 
15 group by pub_name 
16  , book_type 
17/

PUB_ BOOK COUNT(*) 
---- ---- ---------- 
PUB1 MIS   1 
PUB1 JAVA   1 
PUB2 JAVA   1 
PUB3 UNI   2 

4 rows selected. 

希望这有助于。

Regards，
Rob。