检索出现多次的行

Question

假设我有表A和表B，它们之间的关系是1到多，我如何只检索表B中A PK出现多次？的行？作为FK？我不知道我怎么能这样做。

Answer 1

您可以对B行进行分组，并在A的子查询中对其进行计数：

SELECT *
FROM   A
WHERE  A.pk IN (SELECT   fk
                FROM     B
                GROUP BY fk
                HAVING   COUNT(*) > 1)

Answer 2

SELECT fkey，count（*）FROM B WHERE fkey IN（SELECT pkey FROM A）GROUP BY fkey HAVING count（*）＆gt; 1;