When did the violin players perform?
SELECT T3.Date FROM member_attendance AS T1 JOIN member AS T2 ON T1.Member_ID   =   T2.Member_ID JOIN performance AS T3 ON T1.Performance_ID   =   T3.Performance_ID WHERE T2.Role   =   "Violin"
violin players perform refers to the date of the performance where the role is Violin; using JOIN to link tables based on related columns; filtering results based on specific role (Violin);