Question

我正在尝试构建一个返回与特定商机相关联的联系人列表的查询。

我有3个表：联系人，机会和关系（多对多）

联系人

id   name
---------
1   Davey Jones
2   Bob Hope
3   Tiger Woods
4   Hillary Clinton

机会

id    description
------------------
1     visit the locker
2     singing and dancing
3     playing golf
4     laughing and crying

关系

id     firstid     firsttype      secondid     secondtype
---------------------------------------------------------
1      1           contact        1           opportunity
2      3           opportunity    3           contact
3      4           contact        4           opportunity
4      4           opportunity    3           contact

现在，如果我有opportunity_id，我想返回与该机会相关联的所有联系人。

因此，如果opportunity_id = 4，则成功查询的结果应为：

Hillary CLinton
Tiger Woods

但这是我的查询，只返回1条记录：

SELECT
contacts.name
FROM
contacts
INNER JOIN relationships ON contacts.id = relationships.secondid
INNER JOIN opportunities ON opportunities.id = relationships.firstid
where
opportunities.id=4
and (relationships.firsttype='opportunity' and relationships.secondtype='contact')
or (relationships.firsttype='contact' and relationships.secondtype='opportunity')

我被困在如何在这个查询中触发联接。

编辑：我刚刚发现了UNION，然后尝试了这个，它似乎有效：

(select contacts.name from contacts where contacts.id =
    (select secondid as id from relationships  where (firstid = 4 and (firsttype='opportunity' and secondTtpe='contact' ) ) ) )
    UNION
 (select contacts.name from contacts where contacts.id =
    (select firstid as id from relationships where (secondid = 4 and (firsttype='contact' and secondtype='opportunity' ) ) ) )

但这看起来很笨拙。这是解决这个问题的最好方法吗？

Answer 1

试试这个：

SELECT contacts.name FROM contacts
    inner join (
        SELECT * from relationships
        where 
            (firstid = 4 and (firsttype='opportunity' and secondtype='contact' ) )
            or 
            (secondid= 4 and (firsttype='contact' and secondtype='opportunity' ) ) 
    ) rel
    on contacts.id = rel.id;

Answer 2

以简单的方式，您需要更改表relationships的设计，我建议：

<强>关系

id     id_contact     id_opportunity
-------------------------------------
1      1              1
2      3              3
3      4              4
4      3              4

因此，对relationships的更改，您的查询可能如下所示：

SELECT contacts.name 
FROM contacts
INNER JOIN relationships ON contacts.id = relationships.id_contact
INNER JOIN opportunities ON opportunities.id = relationships.id_opportunity
WHERE opportunities.id=4;

您必须记住规范化表格（因此表格relationships必须具有其他表格中的标识符，每个表格只有一个 ...这就是为什么是标识符），并且在many-to-many表格中要小心。

具有反向连接的MySql查询

2 个答案: