MySql 数据库查询用于从每个类别中随机选择？

Question

Table Name : Employee
    +------+------+
    | name | dept |
    +------+------+
    | ABC  | 1    |
    | BCA  | 1    |
    | CYZ  | 2    |
    | CYZ  | 1    |
    | n... | n... |
    +------+------+

Table Name : Department
    +----+-----------+
    | id | dept_name |
    +----+-----------+
    | 1  | YYY       |
    | 2  | ZZZ       |
    | 3  | DDD       |
    +----+-----------+

我必须从表 Employees 中针对每个 dept_name 选择 25 个随机条目。例如。在表 Department 中，有 10 个具有唯一 id 的条目。因此结果查询将返回 25(random) * 10 = 250 行。

到目前为止，我正在计算这个查询，但有些问题。

Select * from Employee where dept in (Select id from Department) RAND;

Answer 1

可能如下所示:

SELECT d.id, GROUP_CONCAT(name) employee_list FROM Department d JOIN (

    SELECT name FROM EMPLOYEE e WHERE d.id = e.dept ORDER BY RAND() LIMIT 25
  ) v

  GROUP BY d.id
  LIMIT 10