如何在外部联接中为表编写条件？

Question

I would like to display all sessions with the date, which is taken from the schedule_session table by joining it, and filtering by class_id.

select * from sessions s 
left join schedule_session ss on ss.session_id = s.id 
where ss.class_id = 5

This query does not return all sessions because I am saying where class_id = 5 so it returns only specific class sessions. Is there any method that I can first get all sessions and show in the date property, and the date from the schedule_session if it exists for that particular session. So in the end I have all sessions but haven't assigned any date for it.

So I want all sessions and show the value of date if it exists for that class, if not show date as null or blank .

Thanks

Answer 1

Not clear description but i think below is your solution.

select * from sessions s 
left join schedule_session ss on ss.session_id = s.id and ss.class_id = 5