php - MYSQL 如果最大 id 有一列为 NULL，则排除行

Question

我正在构建用户工作负载的报告图表，显示事件任务、已暂停和未启动的任务，但在“已暂停”的结果中，我还检索了事件作业

SELECT 'active' AS `status`,COUNT(DISTINCT TA.`task_id`) AS `tasks`,U.uID AS `user_id`,
    CONCAT(U.`firstname`, ' ', U.`lastname`) AS `user`
    FROM `tasks` TA
    INNER JOIN `users` U on U.`uID`=TA.`scheduled_to_user`
    INNER JOIN `ticket` T on T.`tID`=TA.`ticketFK`
    INNER JOIN `task_activity_log` TL ON TL.`task_id`=TA.`task_id`
    INNER JOIN `project` P ON P.`pID`=T.`pFK`
    WHERE TA.`started_on` IS NOT NULL 
    AND TA.`completed_on` IS NULL
    AND TL.`start_ts` IS NOT NULL
    AND TL.`end_ts` IS NULL
    AND T.`closed_on` IS NULL
    GROUP BY U.`uID`
    UNION 
    SELECT 'paused' AS `status`, COUNT(DISTINCT TA.`task_id`) AS `tasks`,U.uID AS `user_id`,
    CONCAT(U.`firstname`, ' ', U.`lastname`) AS `user`
    FROM `tasks` TA
    INNER JOIN `system_users` U on U.`uID`=TA.`scheduled_to_user`
    INNER JOIN `task_activity_log` TL ON TL.`task_id`=TA.`task_id`
    INNER JOIN `icket` T on T.`tID`=TA.`ticketFK`
    INNER JOIN `project` P ON P.`pID`=T.`pFK`
    WHERE TA.`started_on` IS NOT NULL 
    AND TA.`completed_on` IS NULL
    AND T.`closed_on` IS NULL
    AND TL.`start_ts` IS NOT NULL
    AND TL.`end_ts` IS NOT NULL
    GROUP BY U.`uID`
    UNION
    SELECT 'not started' AS `status`, COUNT(DISTINCT TA.`task_id`) AS `tasks`,U.uID AS `user_id`,
    CONCAT(U.`firstname`, ' ', U.`lastname`) AS `user`
    FROM `tasks` TA
    INNER JOIN `users` U on U.`uID`=TA.`scheduled_to_user`
    INNER JOIN `ticket` T on T.`tID`=TA.`ticketFK`
    INNER JOIN `project` P ON P.`pID`=T.`pFK`
    WHERE TA.`started_on` IS NULL 
    AND TA.`completed_on` IS NULL
    AND T.`closed_on` IS NULL
    GROUP BY U.`uID`

task_activity_log 表看起来像这样:

| id | task_id | start_ts                 | end_ts               |
  1       1       2017-02-28 15:47:34         2017-02-28 15:47:34
  2       1       2017-02-28 15:47:34         (NULL)
  3       2       2017-02-28 15:47:34         2017-02-28 15:47:34
  4       2       2017-02-28 15:47:34         2017-02-28 15:47:34

id 2 是一个事件任务。我尝试通过尝试诸如

之类的方法来获取每个任务的最大 ID(最新事件)

LEFT JOIN (SELECT MAX(`id`)AS `max_id`,`task_id` AS `task_id` FROM`task_activity_log`) MA ON MA.`task_id`=TA.`task_id`

或

(SELECT MAX(`id`) FROM`task_activity_log` A1 WHERE A1.`task_id`=TA.`task_id`) AS `max_id`

但我无法正确理解这一点(我想我已经看它太久了)任何帮助将不胜感激

Answer 1

您想要做的是使用其自身的聚合(上次记录的任务事件)来过滤task_activity_log。

你需要的是这样的

select ts.*
from 'task_activity_log' as 'ts'
join (select 'task_id', max('id') as 'id' from 'task_activity_log' group by 'task_id') as 'max_ts'
on ts.'task_id' = max_ts.'task_id' and ts.'id' = max_ts.'id'

这样，您只需考虑引用最新事件的 task_activity_log 行。