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"
Show the dates of performances with attending members whose roles are "Violin".
[Schema (values) (types)]: | performance_attendance |  member : member_id (text) , name (text) , nationality (text) , role (text) | performance : performance_id (text) , date (text) , host (text) , location (text) , attendance (text) | member_attendance : member_id (text) , performance_id (text) , num_of_pieces (text);