如何将 UNION 与 EXISTS 结合起来？

Question

我有一个如下所示的查询：

SELECT PubKey, Title FROM Publication
UNION
SELECT NoteKey, Title, FROM Note

效果很好。当我尝试向其中添加 EXIST 时，我的麻烦就开始了：

SELECT PubKey, Title FROM Publication
UNION
SELECT NoteKey, Title, FROM Note
WHERE EXISTS (SELECT * FROM UserPublication WHERE UserPublication.PubKey = Publication.PubKey)

这会引发此错误：无法绑定多部分标识符“PubKey”。

可以用另一种方式写吗？

Answer 1

该WHERE条款是针对每个人的SELECT，因此您需要将现有的条款移至第一个，SELECT如下所示：

SELECT PubKey, Title FROM Publication
WHERE EXISTS (
    SELECT * 
      FROM UserPublication 
     WHERE UserPublication.PubKey = Publication.PubKey
)
UNION
SELECT NoteKey, Title FROM Note

但是，如果您想WHERE在整个结果集中指定该子句。这必须像这样完成：

SELECT * FROM (
    SELECT PubKey, Title FROM Publication
    UNION
    SELECT NoteKey, Title FROM Note
) AS A
WHERE EXISTS (
    SELECT * 
      FROM UserPublication 
     WHERE UserPublication.PubKey = A.PubKey
)