oracle sql error case when then else

Question

SELECT * 
FROM FirstTable 
WHERE RowProcessed = 'N' 
AND (
     CASE 
      WHEN EXISTS(SELECT top 1 FROM SecondTable) 
      THEN 1 
      ELSE EXISTS(
         SELECT SecondTable.RowProcessed 
         FROM SecondTable 
         WHERE FirstTable.Key = SecondTable.Key 
         AND SecondTable.RowProcessed = 'Y' 
         ) 
     END 
     ) 
AND OtherConditions 

case when then else where where clause。不確定語法。

我想驗證在SecondTable中有行，如果有行檢查另一個條件，這基本上是我想要做的。

Answer 1

也許這是你想要的？如果在SecondTable中有行，那麼請執行第二步：EXISTS：

SELECT * FROM FirstTable 
WHERE RowProcessed = 'N' 
AND (NOT EXISTS (SELECT 1 from SecondTable) 
     OR EXISTS (SELECT 1 FROM SecondTable 
       WHERE FirstTable.Key = SecondTable.Key 
        and SecondTable.RowProcessed = 'Y')) 
AND OtherConditions