php - Need help with this MySQL query. Finding users who are available at a certain time -


here simplified schema of database:

users ------------------------------------ userid | name      | assignable ------------------------------------   5    | john doe  |      1  timeslots ------------------------------------------------------- timeslotid | starttime           | endtime -------------------------------------------------------      3     | 2011-06-30 15:00:00 | 2011-06-30 16:00:00  appointments ------------------------------------ timeslotid | userid ------------------------------------      3     |    5

i have users can assigned timeslots make appointments. need way start start , end time , query users able assigned (assignable flag set 1) , have no time conflicts (appointments overlap) times.

older timeslots in there interested in timeslots or in future.

select * users u     u.assignable = 1     , u.userid not in (        select userid        appointments          join timeslots t on a.timeslotid = t.timeslotid         t.endtime > now()           , t.endtime > @desiredstarttime           , t.starttime < @desiredendtime     )

edit taking cue tandu

i think work, , has added performance benefit of no subqueries:

select * users u         left join appointments on a.userid = u.userid     left join timeslots t on (     a.timeslotid = t.timeslotid         , t.endtime > now()        , t.endtime > @desiredstarttime        , t.starttime < @desiredendtime     )      u.assignable = 1     , t.timeslotid null

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