Description of the illustration first.eps

aggregate_function KEEP
   ( DENSE_RANK FIRST ORDER BY
    expr [ DESC | ASC ]
         [ NULLS { FIRST | LAST } ]
    [, expr [ DESC | ASC ]
            [ NULLS { FIRST | LAST } ]
    ]...
   )
   [ OVER { window_name | { [ window_name ] | [ query_partition_clause ]}  }
 ]