Question

A related example:

table activity
activity id | title
1             a
2             a2
3             b
4             b2

table people
id | parent id | activity id | active

Grab all the people who:

• is in a specific activity without a parent
• is in a specific activity who’s parent is not in the same activity + not in the same related activity (ie: a, a2)

So far I have something less than ideal:

SELECT p.pid FROM people p
left join activity a
on p.activityid = a.activityid
where p.active = 1
and a.title = 'a'
and EXISTS (
    SELECT p1.pid from people p1
    left join activity a1
    on p1.activityid = a1.activityid
    where p.parentid = p1.id
    and a1.activityid != p.activityid
    or p.parentid = 0
)

This doesn’t account for parentids not ‘a2’ or ‘b2’ etc..
The thing is I have the target activity id I want, but not the related activity, so I figured I’d somehow use the title instead?

Answer 1

You don’t need a outer join. The not exixts clause will filer out someone without parents.

SELECT p.pid 
FROM people p,  activity a 
WHERE p.activityid = a.activityid 
AND p.active = 1 AND a.title = 'a' 
AND NOT EXISTS
( SELECT 1 FROM people pp, activity pa
  WHERE p.parentid = pp.id AND pp.activityid = pa.activityid
  AND pa.title NOT LIKE a.title||'%'
);