oracle sql错误案例当其他时候

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

案例在where子句中的其他地方。不确定语法。

我想验证SecondTable中是否有行，如果有行检查另一个条件，那基本上就是我想要做的。

Answer 1

也许这就是你想要的？如果SecondTable中有行，则执行第二个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