这回答了问题的原始版本。
Impala 并不完全支持 range between . 不幸的是，这并没有留下很多选择。一是使用 lag() 有很多明确的逻辑：

select t.*,
       ( (case when lag(date, 6) over (partition by client_id order by date) = date - interval 6 day
               then lag(connections, 6) over (partition by client_id order by date)
               else 0
          end) +
         (case when lag(date, 5) over (partition by client_id order by date) = date - interval 6 day
               then lag(connections, 5) over (partition by client_id order by date)
               else 0
          end) +
         (case when lag(date, 4) over (partition by client_id order by date) = date - interval 6 day
               then lag(connections, 4) over (partition by client_id order by date)
               else 0
          end) +
         (case when lag(date, 3) over (partition by client_id order by date) = date - interval 6 day
               then lag(connections, 3) over (partition by client_id order by date)
               else 0
          end) +
         (case when lag(date, 2) over (partition by client_id order by date) = date - interval 6 day
               then lag(connections, 2) over (partition by client_id order by date)
               else 0
          end) +
         (case when lag(date, 1) over (partition by client_id order by date) = date - interval 6 day
               then lag(connections, 1) over (partition by client_id order by date)
               else 0
          end) +
         connections
        ) as connections_within_6_days         
from t;

不幸的是，这并不能很好地概括。如果你想要一个大范围的天数，你可能想问另一个问题。