Question

我有3张桌子：冠军，角色，champs_to_roles

champs_to_roles表看起来像这样：

|ID_champ|ID_role|
 ----------------
|       2|      2|
|       4|      5|
|       5|      3|
|       3|      2|
|       1|      1|
|       1|      2|

我正在尝试选择ID_champ WHERE ID_role = 1 AND ID_role = 2.

此时我有以下代码：

SELECT DISTINCT `c`.`name`
FROM `champions` AS c,
(
    SELECT `ID_champ`
    FROM `champs_to_roles`
    WHERE `ID_role` IN(1,2)
) AS r
WHERE `r`.`ID_champ` = `c`.`ID`

但是，这会返回ID_champ，ID_role = 1或Id_role = 2或两者都

我如何获取我需要的东西？

非常感谢：）

Answer 1

对关联表使用两个内部联接 - 每个角色类型一个：

SELECT c.name
FROM champions c
JOIN champs_to_roles ctr1 ON ctr1.ID_champ = c.id AND ctr1.ID_role = 1
JOIN champs_to_roles ctr2 ON ctr2.ID_champ = c.id AND ctr2.ID_role = 2

通过使用内部连接， champs_to_roles中的行必须存在才能返回冠军。

DISTINCT关键字是免费的，因为你不需要它（除非你的关联表中有重复的条目，这似乎不太可能，如果可能的话，设计也很糟糕）

Answer 2

我可能会选择Bohemian的解决方案，但为了完整性，还可以使用计数并检查从子选择返回的角色数

SELECT c.name
FROM champions AS c
INNER JOIN 
(
    SELECT ID_champ, COUNT(DISTINCT ID_role) AS NumRole
    FROM champs_to_roles
    WHERE ID_role IN(1,2)
    GROUP BY ID_champ
) AS r 
ON r.ID_champ = c.ID AND NumRole = 2

（这也可以在没有subselect的情况下完成，但如果你没有返回需要分组的列等，那么它的可读性就会降低）

Answer 3

您可以尝试以下方式：

Select 
    c.name
from
    champions c
where
    exists( select 
            1
        from
            champs_to_roles ctr1
        where
            ctr1.ID_champ = c.ID
                and exists( select 
                    1
                from
                    champs_to_roles ctr2
                where
                    ctr2.ID_champ = ctr1.ID_champ
                        and ctr2.ID_role <> ctr1.ID_role))

Answer 4

试试这个，

SELECT DISTINCT c.name
FROM champions AS c,
(
    SELECT c1.ID_champ
    FROM champs_to_roles c1, champs_to_roles c2
    WHERE c1.ID_role=1 and c2.ID_role=2 
    AND c1.ID_champ=c2.ID_champ
) AS r
WHERE r.ID_champ = c.ID

WHERE子句需要多个值？

4 个答案: