and { only { filter_eq { filter_eq { all_rows ; region ; africa } ; joined opec ; 1969 } } ; eq { hop { filter_eq { filter_eq { all_rows ; region ; africa } ; joined opec ; 1969 } ; country } ; algeria } } = true
select the rows whose region record fuzzily matches to africa . among these rows , select the rows whose joined opec record is equal to 1969 . there is only one such row in the table . the country record of this unqiue row is algeria .