HIVE左连接似乎返回了错误的结果

Question

我正在检查报告中的一些数据错误，我遇到了左连接的问题。

我尝试将查询重写为非常简单的原理图代码。第一个查询返回'foo'，第二个没有。唯一的区别仅在于on条件，两个选择都应返回零线。谢谢你，马丁

SELECT 'foo'
FROM
  (SELECT
     'A' AS a,
     'B' AS b) X
  LEFT JOIN
  (SELECT
     'C' AS a,
     'B' AS b) Y
    ON X.a = Y.a AND X.b = Y.b
WHERE Y.b IS NOT NULL;    

SELECT 'bar'
FROM
  (SELECT
     'A' AS a,
     'B' AS b) X
  LEFT JOIN
  (SELECT
     'C' AS a,
     'B' AS b) Y
    ON X.a = Y.a
WHERE Y.b IS NOT NULL;