Question

我有一个像这样的桌面设计

person_id   |   department
1           |   a
1           |   b
2           |   a
2           |   c
3           |   b
3           |   a

并希望查询返回属于a和b部门的所有person_id。我认为这将是

的内容

select person_id from table group by person_id having ....

但无法弄明白。有谁知道我怎么能这样做？

编辑：我发现我可以做到以下几点。但它似乎是一个黑客。

select person_id from table where department='A' or department='B' 
     group by person_id having count(1) > 1

Answer 1

SELECT
  person_id
FROM
  yourTable
WHERE
     department = 'a'
  OR department = 'b'
GROUP BY
  person_id
HAVING
  COUNT(DISTINCT department) = 2

注意：只有当一个人可以多次成为同一部门的成员时才需要DISTINCT。

Answer 2

您还可以使用子查询来实现此目的：

SELECT person_id 
FROM table t1 
WHERE t1.department = 'a' 
    AND EXISTS (SELECT 1 
            FROM table t2 
            WHERE t2.department = 'b' 
                AND t1.person_id = t2.person_id`)

查找匹配多个行值的外键

2 个答案: