GROUP BY 可能的序列

Question

我有一个包含以下数据的表，使用 Postgres 9.6：

log_id | 序列 | made_at（时间戳）
206480 1 1
206480 1 2
206480 2 3
206480 3 4
206480 1 5
206480 2 6
206480 4 7
206480 5 8
206480 1 9
206480 2 10
206481 1 11
206481 2 12
206481 3 13
206481 4 14

我必须对 ID 进行分组和聚合，以便获得一系列可能的序列。最后，我希望数据看起来像这样：

log_id | 序列
206480 {1,1,2,3}
206480 {1,2,4,5}
206480{1,2}
206481 {1,2,3,4}

在以下情况下，我想要一个新行（带有序列）：

• 的log_id变化; 或者
• 下一个序列号低于当前序列号。

还有另一列指定排序（时间戳），但它在另一个表中（我加入它们并使用该时间戳）。为了使事情更容易，我省略了它，但我们可以假设该列名为made_at.

Answer 1

select      log_id
           ,array_agg (sequence)

from       (select      log_id 
                       ,sequence
                       ,count (is_restart) over
                        (
                            partition by    log_id 
                            order by        made_at
                        ) as restart_id

            from        (select      made_at
                                    ,log_id 
                                    ,sequence
                                    ,case 
                                         when sequence <
                                              lag (sequence) over
                                              (
                                                  partition by    log_id 
                                                  order by        made_at
                                              ) 
                                         then 1
                                     end            is_restart

                         from        logs
                         ) l
            ) l

group by    log_id      
           ,restart_id

order by    log_id      
           ,restart_id
;

select      log_id
           ,array_agg (sequence)

from       (select      log_id 
                       ,sequence
                       ,count (is_restart) over
                        (
                            partition by    log_id 
                            order by        made_at
                        ) as restart_id

            from        (select      made_at
                                    ,log_id 
                                    ,sequence
                                    ,case 
                                         when sequence <
                                              lag (sequence) over
                                              (
                                                  partition by    log_id 
                                                  order by        made_at
                                              ) 
                                         then 1
                                     end            is_restart

                         from        logs
                         ) l
            ) l

group by    log_id      
           ,restart_id

order by    log_id      
           ,restart_id
;

演练

• 通过将当前序列与先前序列 ( LAG)进行比较来识别重新启动。

  select      made_at
             ,log_id 
             ,sequence
  
             ,case 
                  when sequence <
                       lag (sequence) over
                       (
                           partition by    log_id 
                           order by        made_at
                       ) 
                  then 1
              end            is_restart
  
  from        logs
  

  +--------+-----------+
  | log_id | array_agg |
  +--------+-----------+
  | 206480 | {1,1,2,3} |
  +--------+-----------+
  | 206480 | {1,2,4,5} |
  +--------+-----------+
  | 206480 | {1,2}     |
  +--------+-----------+
  | 206481 | {1,2,3,4} |
  +--------+-----------+
  

• 执行重新启动 ( is_restart) 的“运行计数”（类似于“运行总数” ）。
  属于同一组的行将具有相同的计数（AKA restart_id）。
  中的“Order by”COUNT暗示range between unbounded preceding and current row

  select      log_id 
             ,sequence
             ,count (is_restart) over
              (
                  partition by    log_id 
                  order by        made_at
              ) as group_id
  
  from        (...) l
  

  select      made_at
             ,log_id 
             ,sequence
  
             ,case 
                  when sequence <
                       lag (sequence) over
                       (
                           partition by    log_id 
                           order by        made_at
                       ) 
                  then 1
              end            is_restart
  
  from        logs
  

• 通过集团log_id和restart_id和总序列

  select      log_id
             ,array_agg (sequence)
  
  from       (...) l
  
  group by    log_id      
             ,restart_id
  
  order by    log_id      
             ,restart_id
  ;
  

  +---------+--------+----------+------------+
  | made_at | log_id | sequence | is_restart |
  +---------+--------+----------+------------+
  | 1       | 206480 | 1        |            |
  +---------+--------+----------+------------+
  | 2       | 206480 | 1        |            |
  +---------+--------+----------+------------+
  | 3       | 206480 | 2        |            |
  +---------+--------+----------+------------+
  | 4       | 206480 | 3        |            |
  +---------+--------+----------+------------+
  | 5       | 206480 | 1        | 1          |
  +---------+--------+----------+------------+
  | 6       | 206480 | 2        |            |
  +---------+--------+----------+------------+
  | 7       | 206480 | 4        |            |
  +---------+--------+----------+------------+
  | 8       | 206480 | 5        |            |
  +---------+--------+----------+------------+
  | 9       | 206480 | 1        | 1          |
  +---------+--------+----------+------------+
  | 10      | 206480 | 2        |            |
  +---------+--------+----------+------------+
  | 11      | 206481 | 1        |            |
  +---------+--------+----------+------------+
  | 12      | 206481 | 2        |            |
  +---------+--------+----------+------------+
  | 13      | 206481 | 3        |            |
  +---------+--------+----------+------------+
  | 14      | 206481 | 4        |            |
  +---------+--------+----------+------------+