MySQL Left Join Count活动并返回null

Question

Trying to get this mysql query to work.

Explanation: There are two tables, one with all projects with org id columns, the second has all activities with column projectid that relates to the project table. I would like to count all activities within the activities table that has the userid and is active with 1. But here comes the tricky part, I cannot get working. It does not collect the projects that are missing in activities table and present these with count 0. I would like to show all project that correspond with a unique projectid within bo

SELECT p1.`id` AS projectid ,count(a1.`id`) AS activitiescount ,a1.`userid` AS userid ,p1.`orgid` AS orgid  
FROM `projects` AS p1 
LEFT JOIN `activities` AS a1 
ON p1.`id`=a1.`projectid` 
WHERE p1.`orgid`=3 
AND a1.`userid` = 26 
AND a1.`active`=1 
OR a1.`id` IS null 
GROUP BY p1.`id` 
ORDER BY p1.`name` DESC

Gives:

As you can see, the is not correct with 6 and 2 for example. Please help. Thank you.

Answer 1

Untested:

Moved limits on Activities to the join.

Also the OR brought back more than you wanted, by moving the where clause around that problem should be resolved as well.

Standard Approach:

SELECT p1.`id` AS projectid 
     , count(a1.`id`) AS activitiescount 
     , a1.`userid` AS userid 
     , p1.`orgid` AS orgid  
FROM `projects` AS p1 
LEFT JOIN `activities` AS a1 
  ON p1.`id`=a1.`projectid` 
 AND a1.`userid` = 26 
 AND a1.`active`=1 
WHERE p1.`orgid`=3 
GROUP BY p1.`id` 
ORDER BY p1.`name` DESC

your approach w/ ()'s correctly placed.

SELECT 
    p1.`id` AS projectid 
    ,count(a1.`id`) AS activitiescount 
    ,a1.`userid` AS userid 
    ,p1.`orgid` AS orgid  

FROM `projects` AS p1 
LEFT JOIN `activities` AS a1 ON p1.`id`=a1.`projectid` 

WHERE p1.`orgid`=3 
  AND ((a1.`userid` = 26 AND a1.`active`=1)  OR a1.`id` IS null) 
GROUP BY p1.`id` 
ORDER BY p1.`name` DESC

----Update to simulate full outer join per comment.

SELECT * 
FROM (
SELECT p1.`id` AS projectid 
     , count(a1.`id`) AS activitiescount 
     , a1.`userid` AS userid 
     , p1.`orgid` AS orgid  
FROM `projects` AS p1 
LEFT JOIN `activities` AS a1 
  ON p1.`id`=a1.`projectid` 
 AND a1.`userid` = 26 
 AND a1.`active`=1 
WHERE p1.`orgid`=3 
GROUP BY p1.`id` 
UNION  
SELECT p1.`id` AS projectid 
     , count(a1.`id`) AS activitiescount 
     , a1.`userid` AS userid 
     , p1.`orgid` AS orgid  
FROM `projects` AS p1 
RIGHT JOIN `activities` AS a1 
  ON p1.`id`=a1.`projectid` 
 AND p1.`orgid`=3 
WHERE a1.`userid` = 26 
 AND a1.`active`=1 
GROUP BY p1.`id`)
ORDER BY p1.`id`,A1.ID -- assumes A1.ID exists and you want to order in that fashion.