Question

MySQL Query Language Please help

Find the ids of users who own at least one of every kind of observer. Note that a user can have multiple observers of the same type, and note also that new observers can be added at any time (so don’t use any constants in your query, e.g., do not assume static knowledge of the set of all possible observer kinds)

Here are the attributes:

tnum number observation_id PHLG obs observationid PHLogger address street address_state diastolic number tnum number User manufacturer pswd string

Answer 1

In orde4 to achieve we can use observable table which contain observer_id and corresponding kind. In observable table one observer_id have aleast one kind. If onserver_id is not available in observable table. Below is query

select Observer_id from observable group by observer_id having count(kind)>=1;