and { only { filter_eq { all_rows ; year ; 2002 } } ; eq { hop { filter_eq { all_rows ; year ; 2002 } ; event } ; ozzfest 2002 } } = true
select the rows whose year record is equal to 2002 . there is only one such row in the table . the event record of this unqiue row is ozzfest 2002 .