2

这有效：

 SELECT (CASE
             WHEN x = 'value' THEN
              a.col1
             ELSE
              nvl(a.col1, a.col2)
           END)
      FROM table1 a
     WHERE a.this = 'that'
     GROUP BY (CASE
                WHEN x = 'value'  THEN
                 a.col1
                ELSE
                 nvl(a.col1, a.col2)
              END)

但是尝试让 case 语句执行 IN 语句（在此处尝试更动态的 sql），以下代码会导致ORA-00979错误。

SELECT (CASE
         WHEN x IN (SELECT me FROM here WHERE this = 'example') THEN
          a.col1
         ELSE
          nvl(a.col1, a.col2)
       END)
  FROM table1 a
 WHERE a.this = 'that'
 GROUP BY (CASE
            WHEN x IN (SELECT me FROM here WHERE this = 'example') THEN
             a.col1
            ELSE
             nvl(a.col1, a.col2)
          END)

是否有可能使这项工作或有替代方案？谢谢。——乔纳斯

Benoit：这是根据您的 sql 重新创建错误的修改后的 sql：

select (case when a.y IN (select 'A'||ROWNUM from dual where rownum=1) then 1 else 0 end)
from (SELECT 'A'||ROWNUM y, 'B' x FROM DUAL CONNECT BY ROWNUM <= 3) a where x = 'B'
group by (case when a.y IN (select 'A'||ROWNUM from dual where rownum=1) then 1 else 0 end)
;

基本上缺少的是 FROM 表应该有多个值，并且在 CASE 语句中引用了一个列。

4

2 回答 2

2

我无法通过以下请求（工作）重现此错误：

select (case when 'X' IN (select dummy from dual where rownum=1) then 1 else 0 end)
from dual
where dummy = 'X'
group by (case when 'X' IN (select dummy from dual where rownum=1) then 1 else 0 end)
;

尝试：

WITH table1_extended AS (
   SELECT a.*, CASE WHEN x IN .... END "condition"
     FROM table1 a
)
SELECT b."condition"
  FROM table1_extended b
 WHERE b.this = 'that'
 GROUP BY b."condition"
于 2010-09-29T07:59:50.860 回答
1

您是否有理由不能将子选择移动到连接中？从您对@Benoit 测试用例的调整版本中，您可以执行以下操作：

select case when a.y = b.z then 1 else 0 end, count(*)
from (select 'A'||rownum y, 'B' x from dual connect by rownum <= 3) a,
    (select 'A'||rownum z from dual where rownum=1) b
where a.x = 'B'
group by case when a.y = b.z then 1 else 0 end;

这给出了（10g）：

CASEWHENA.Y=B.ZTHEN1ELSE0END COUNT(*)               
---------------------------- ---------------------- 
1                            1                      
0                            2

不完全相信这会给出你想要的答案，但很难说，因为它是如此简化，并且可能是一个起点。

编辑似乎这确实太简单了。另一种可能的解决方案看起来也太简单但可能会奏效，是从另一端处理这个问题，然后case在select聚合函数中创建：

SELECT MIN(CASE
         WHEN x IN (SELECT me FROM here WHERE this = 'example') THEN
          a.col1
         ELSE
          nvl(a.col1, a.col2)
       END)
  FROM table1 a
 WHERE a.this = 'that'
 GROUP BY (CASE
            WHEN x IN (SELECT me FROM here WHERE this = 'example') THEN
             a.col1
            ELSE
             nvl(a.col1, a.col2)
          END)
于 2010-09-29T09:18:14.137 回答