sql - 根据特定标准对记录进行分组并查找最大值

Question

我有一个veh_speed包含字段 vid 的表, date_time , speed , status 。我的目标是获取速度大于 30 的车辆的持续时间( start_date_time 和 end_date_time )。目前我正在使用 PL/SQL 生成报告。 。是否有可能与SQL有关。如果能够获得范围内的 max_speed，那就太好了。

我的表格如下:

VID  START_DATE_TIME        SPEED  STATUS
---  -------------------    -----  ------
1   15/01/2014 10:00:05     0      N
1   15/01/2014 10:00:10    10      Y 
1   15/01/2014 10:00:15    30      Y
1   15/01/2014 10:00:20    35      Y
1   15/01/2014 10:00:25    45      Y
1   15/01/2014 10:00:27    10      Y
1   15/01/2014 10:00:29     0      Y
1   15/01/2014 10:00:30    20      Y
1   15/01/2014 10:00:35    32      Y
1   15/01/2014 10:00:40    33      Y
1   15/01/2014 10:00:45    35      Y
1   15/01/2014 10:00:50    38      Y
1   15/01/2014 10:00:55    10      Y

我想得到以下输出:

VID   START_DATE_TIME          END_DATE_TIME          MAX_SPEED
---   ---------------          -------------          ---------
1    15/01/2014 10:00:15     15/01/2014 10:00:25      45
1    15/01/2014 10:00:35     15/01/2014 10:00:50      38

这是表创建脚本:

CREATE TABLE veh_speed(vid NUMBER(3), 
             date_time DATE, 
             speed NUMBER(3), 
             status CHAR(1));

INSERT ALL
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:05', 'dd/mm/yyyy hh24:mi:ss'),  0,  'N')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:10', 'dd/mm/yyyy hh24:mi:ss'), 10, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:15', 'dd/mm/yyyy hh24:mi:ss'), 30, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:20', 'dd/mm/yyyy hh24:mi:ss'), 35, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:25', 'dd/mm/yyyy hh24:mi:ss'), 45, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:27', 'dd/mm/yyyy hh24:mi:ss'), 10, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:29', 'dd/mm/yyyy hh24:mi:ss'),  0, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:30', 'dd/mm/yyyy hh24:mi:ss'), 20, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:35', 'dd/mm/yyyy hh24:mi:ss'), 32, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:40', 'dd/mm/yyyy hh24:mi:ss'), 33, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:45', 'dd/mm/yyyy hh24:mi:ss'), 35, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:50', 'dd/mm/yyyy hh24:mi:ss'), 38, 'Y')
     INTO veh_speed VALUES(1, to_date('15/01/2014 10:00:55', 'dd/mm/yyyy hh24:mi:ss'), 10, 'Y')
SELECT * FROM dual;

我希望我的问题说清楚了。

提前致谢。

Answer 1

您可以使用分析函数将记录分组为速度为 30 或更高的 block :

select vid, date_time, speed, status,
  case when speed >= 30 then 30 else 0 end as speed_limit,
  row_number() over (partition by vid order by date_time)
    - row_number() over (
      partition by vid, case when speed >= 30 then 30 else 0 end
      order by date_time) as chain
from veh_speed;

      VID DATE_TIME                SPEED STATUS SPEED_LIMIT      CHAIN
---------- ------------------- ---------- ------ ----------- ----------
         1 15/01/2014 10:00:05          0 N                0          0 
         1 15/01/2014 10:00:10         10 Y                0          0 
         1 15/01/2014 10:00:15         30 Y               30          2 
         1 15/01/2014 10:00:20         35 Y               30          2 
         1 15/01/2014 10:00:25         45 Y               30          2 
         1 15/01/2014 10:00:27         10 Y                0          3 
         1 15/01/2014 10:00:29          0 Y                0          3 
         1 15/01/2014 10:00:30         20 Y                0          3 
         1 15/01/2014 10:00:35         32 Y               30          5 
         1 15/01/2014 10:00:40         33 Y               30          5 
         1 15/01/2014 10:00:45         35 Y               30          5 
         1 15/01/2014 10:00:50         38 Y               30          5 
         1 15/01/2014 10:00:55         10 Y                0          7 

我不能将使用两个 row_number() 调用来生成记录链的技巧归功于我，不幸的是，我在某个地方找到了它(可能是 here )。 chain 的实际值并不重要，只是它们在每个 vid 中都是唯一的，并且对于符合您的条件的连续记录 block 中的所有记录而言都是相同的。

您只对“速度限制”为 30 的相关记录链感兴趣(这很容易是 Y/N 标志或其他)，因此您可以使用它并过滤掉那些链条速度小于30；然后使用普通的聚合函数来得到你想要的:

select vid,
  min(date_time) as start_date_time,
  max(date_time) as end_date_time,
  max(speed) as max_speed
from (
  select vid, date_time, speed, status,
    case when speed >= 30 then 30 else 0 end as speed_limit,
    row_number() over (partition by vid order by date_time)
      - row_number() over (
        partition by vid, case when speed >= 30 then 30 else 0 end
        order by date_time) as chain
  from veh_speed
)
where speed_limit = 30
group by vid, chain
order by vid, start_date_time;

       VID START_DATE_TIME     END_DATE_TIME        MAX_SPEED
---------- ------------------- ------------------- ----------
         1 15/01/2014 10:00:15 15/01/2014 10:00:25         45 
         1 15/01/2014 10:00:35 15/01/2014 10:00:50         38 

SQL Fiddle .