and { only { filter_eq { all_rows ; weight ( kg ) ; 59 } } ; eq { hop { filter_eq { all_rows ; weight ( kg ) ; 59 } ; distance } ; 1000 m } } = true
select the rows whose weight  kg  record is equal to 59 . there is only one such row in the table . the distance record of this unqiue row is 1000 m .