mysql - 连接和多重和条件

Question

我有用户表

ID     NAME
1      John
2      Mike
3      Jack

以及包含属性和用户 ID 的表

USER   ATTRIBUTE
1      1
1      2
2      4

我需要选择具有属性 1 AND 2 的所有用户(因此，在此示例中为用户 #1 John)。属性可以多于两个。

我试过了

SELECT * FROM user u LEFT JOIN attributes a ON u.id = a.user 
WHERE a.attribute = 1 AND a.attribute = 2

但当然它不起作用..

Answer 1

您需要结合使用 IN() 和 GROUP BY ... HAVING 来实现此目的。如果您只需要用户 ID，也无需加入。所以类似:

SELECT user, COUNT(attribute) AS attribute_count
FROM attributes
WHERE attribute IN(...) /* include your set of attributes here */
GROUP BY user
HAVING attribute_count = ? /* include number equal to number of attribute ID's in IN() above */

如果您需要用户 ID 和名称，您只需将从上述查询派生的记录集作为过滤器加入到用户表中即可:

SELECT user.id, user.name
FROM user
INNER JOIN
  (
    SELECT user, COUNT(attribute) AS attribute_count
    FROM attributes
    WHERE attribute IN(...) /* include your set of attributes here */
    GROUP BY user
    HAVING attribute_count = ? /* include number equal to number of attribute ID's in IN() above */
  ) AS filter
  ON user.id = filter.user