PQL For distinct activities in a case, happening at the same time.

I have a table, for CaseIDs (1,2,3...) and some Activities (A,B,C….). The activities might be repeated in a case or they can be unique. and a TimeStamp column corresponding to the caseid and activity. 
i need to write a query where in a case there are 7 distinct activities and all of them must happen in the same timestamp. 
kindly help me with this.