Question

I am not an expert on SQL, so I am asking here some help about the following case :

I have 2 tables; 1 table “task” (ID,TITLE,CREATEDAT) and 1 table “activity” (ID,TASK_ID,TITLE,CREATEDAT) where CREATEDAT are a DATETIME column.

I would like to list the tasks ordering by last CREATEDAT column, in task and activity! I mean, have the most recent task (CREATEDAT AND which have the most recent activity, such an union of task & activity table…) but I have really no idea of how to process?

Thanks you for your help!

Answer 1

To order tasks by most recent activity or creation date if there is no activity on the task:

SELECT t.id, t.title 
  FROM task AS t
    LEFT JOIN activity AS a ON t.id=a.task_id
  GROUP BY t.id
  ORDER BY COALESCE(MAX(a.createdat), t.createdat) DESC