Oracle CASE WHEN - ORA-00936：缺少表达式

Question

我是 oracle 新手，下面是我的 SQL。

SELECT * FROM TABLE1 WHERE COLUMN1 = 'YES'
AND COLUMN2 IN (


CASE WHEN EXISTS(SELECT * FROM TABLE1 WHERE COLUMN1 = 'YES' AND COLUMN2 NOT LIKE '%NO%') 
 THEN 
   SELECT COLUMN2 FROM TABLE1 WHERE COLUMN1 = 'YES' AND COLUMN2 NOT LIKE '%YES%'
 ELSE 
   SELECT COLUMN2 FROM TABLE1 WHERE COLUMN1 = 'YES' AND COLUMN2 NOT LIKE '%YES%'  END)

它给出 ORA-00936: 在 then 语句中缺少表达式。我做错了什么？

Answer 1

THEN 和ELSE 之后的子查询必须用括号括起来：

SELECT * FROM TABLE1 WHERE COLUMN1 = 'YES'
AND COLUMN2 IN (
  CASE 
    WHEN EXISTS (SELECT * FROM TABLE1 WHERE COLUMN1 = 'YES' AND COLUMN2 NOT LIKE '%NO%') 
      THEN (SELECT COLUMN2 FROM TABLE1 WHERE COLUMN1 = 'YES' AND COLUMN2 NOT LIKE '%YES%')
    ELSE (SELECT COLUMN2 FROM TABLE1 WHERE COLUMN1 = 'YES' AND COLUMN2 NOT LIKE '%YES%')
  END
)

仅当这些子查询返回的行数不超过 1 行时，这才有效。
此外，两个子查询是相同的。这是笔误吗？
并且IN 可以更改为=，因为CASE 只返回1 个值。