将组中的最大值附加到结果的每一行？

Question

我有类似下面的数据库结构：应用服务 table :

+-----+--------------+----------+---------------+
|  id | name         | status   | application_id
|  1  | Service 1    |  1       |     24
|  2  | Service 2    |  2       |     24
|  3  | Service 3    |  3       |     25
+-----+--------------+----------+----------------

还有其他 table 具有状态定义：客户状态

+------------+--------------+----------+-----------+
|  status_id | name         | level    | is_closed
|  1         | Status 1     |  2       |     1
|  2         | Status 2     |  1       |     0
|  3         | Status 3     |  3       |     1     
+------------+--------------+----------+----------

ApplicationServices 的每一行的状态计算为按 application_id 分组的记录中的最大级别状态。

因此，要从 ApplicationServices 中获取所有具有状态的记录，结果将如下所示：

+-----+--------------+----------+----------------+-------------+-----------
|  id | name         | status   | application_id | status_name | is_closed
|  1  | Service 1    |  1       |     24         |  Status 1   |    1
|  2  | Service 2    |  2       |     24         |  Status 1   |    1
|  3  | Service 3    |  3       |     25         |  Status 3   |    1
+-----+--------------+----------+----------------+-------------+-----------

是否有有效的方法将按 application_id 分组的 max(level) 结果附加到结果集的每一行？

Answer 1

试试这个：

SELECT A.id, A.name, A.status, A.application_id, CS.name AS status_name, CS.is_closed
FROM ApplicationService A
INNER JOIN (SELECT AA.application_id, MAX(CS.level) AS maxLevel
            FROM ApplicationService AA
            INNER JOIN CustomerStatus CS ON AA.status = CS.status_id
            GROUP BY AA.application_id
          ) AS AA ON A.application_id = AA.application_id 
INNER JOIN CustomerStatus CS ON AA.maxLevel = CS.level;

Answer 2

See working SQLfiddle here.

您可能必须执行子查询。子查询只是将两个表连接在一起，grouping/collapsing by application_id 然后获取最大的 is_closed 值：

SELECT
     t1.status AS `status`,
     t1.application_id AS `app_id`,
     MAX(t2.is_closed) AS `max_is_closed`
   FROM applicationstatus AS t1
  LEFT JOIN customerstatus AS t2 ON
    t1.status = t2.status_id
  GROUP BY t1.application_id

当您合并子查询时，最大 is_closed 值应该可以通过 max_is_closed 别名访问：

SELECT
  t1.id AS id,
  t1.name AS name,
  t1.status AS `status`,
  t1.application_id AS application_id,
  t2.name AS status_name,
  t3.max_is_closed
FROM applicationstatus AS t1
LEFT JOIN customerstatus AS t2 ON
  t1.status = t2.status_id
LEFT JOIN
  (SELECT
     t1.status AS `status`,
     t1.application_id AS `app_id`,
     MAX(t2.is_closed) AS `max_is_closed`
   FROM applicationstatus AS t1
  LEFT JOIN customerstatus AS t2 ON
    t1.status = t2.status_id
  GROUP BY t1.application_id) AS t3 ON
  t1.application_id = t3.app_id

查询的输出：

将组中的最大值附加到结果的每一行？

Attach max from group to every row of results ?

mysql

sql

select

group-by

greatest-n-per-group