sql - SQL 比较表中的信息

Question

我想知道如何比较两条信息，例如我的查询中有两列：surname和forename. 我如何检查列中是否forename存在，surname反之亦然？

到目前为止，我已经创建了两个临时表，一个只选择surname，另一个选择所有其他信息。我打算通过加入来比较它们，但我没有运气。

Answer 1

就像是：

Select u1.Surname, u1.Forename,
    (select count(0) from users u2 where u1.surname = u2.forename) as CountWhereForenameEqualsMySurname,
     (select count(0) from users u2 where u1.forename = u2.surname ) as CountWhereSurnameEqualsMyForename
    From users u1

Answer 2

在不知道表结构的情况下，编写查询有点困难。但我会做这样的事情；根据surname等于. 将表连接到自身forename。

SELECT
    t1.forename as foreName1,
    t1.surname as surName1,
    t2.forename as foreName2,
    t2.surname as surName2
FROM
    tableName as t1 INNER JOIN tablename as t2
        ON
            t1.surname = t2.forename