Question

我的表中充满了来自外部来源的事件，例如：

SELECT target_type, timer_type, event_happened_at
FROM tracked_events 
ORDER BY event_happened_at ASC;


TARGET_TYPE  TIMER_TYPE    EVENT_HAPPENED_AT
"JOB",       "START",      "2018-11-06 06:00:00+00"
"JOB",       "STOP",       "2018-11-06 10:30:00+00"
"PAUSE",     "START",      "2018-11-06 10:30:00+00"
"PAUSE",     "STOP",       "2018-11-06 11:00:00+00"
"JOB",       "START",      "2018-11-06 11:00:00+00"
"JOB",       "STOP",       "2018-11-06 15:00:00+00"

我们可以将逻辑分组分为三行：

TYPE   START                   END
JOB,   2018-11-06 06:00:00+00, 2018-11-06 10:00:00+00
PAUSE, 2018-11-06 10:00:00+00, 2018-11-06 11:00:00+00
JOB,   2018-11-06 11:00:00+00, 2018-11-06 15:00:00+00

我正在尝试找出一种在SQL中执行此分组的好方法。事件类型是预定义的，并保证以“逻辑方式”发送（即，在JOB / END之前不会发生PAUSE / START，并且保证所有事件都存在开始/结束）。

因此，基本上，如果我看到JOB / START，则需要查找下一个JOB / END，同样地，对于PAUSE / START到PAUSE / END也是如此。

我可以看到一个查询，其中我仅查找START事件，并执行子查询以找到其对应的END：

WITH starts AS (
    SELECT session_id, target_type, timer_type, event_happened_at
    FROM received_session_events 
    WHERE session_id = 266
    AND TIMER_TYPE = 'START'
    ORDER BY event_happened_at ASC
)

SELECT target_type, event_happened_at AS started_at,
       (
         SELECT event_happened_at 
         FROM received_session_events end_event
         WHERE session_id = starts.session_id 
         AND   timer_type = 'STOP' AND end_event.target_type = starts.target_type
         AND   end_event.event_happened_at > starts.event_happened_at
         ORDER BY event_happened_at ASC
         LIMIT 1
       ) AS ended_at
FROM starts

这可以正常工作，并且给出正确的结果，但是似乎有些效率低下。添加索引是我没有探索过的选项（除了出现在WHERE子句中的显而易见的索引之外，我也不知道从哪里开始。）

Answer 1

假设数据遵循事件目标和时间的“逻辑顺序”，请考虑添加行号并运行移位的自我联接：

WITH s2 AS
 (SELECT *, ROW_NUMBER() OVER() As ROW_NUM
  FROM received_session_events)         

SELECT CASE 
            WHEN s1.TARGET_TYPE = 'DEAL' 
            THEN 'JOB' 
            ELSE s1.TARGET_TYPE
       END AS "TYPE", s1.EVENT_HAPPENED_AT AS "START", s2.EVENT_HAPPENED_AT AS "END"
FROM s2 AS s1
JOIN 
   s2 
 ON s1.TARGET_TYPE = s2.TARGET_TYPE AND s1.ROW_NUM = s2.ROW_NUM - 1
ORDER BY s1.EVENT_HAPPENED_AT;

--   TYPE                    START                     END
--    JOB   2018-11-06 06:00:00+00  2018-11-06 10:30:00+00
--  PAUSE   2018-11-06 10:30:00+00  2018-11-06 11:00:00+00
--    JOB   2018-11-06 11:00:00+00  2018-11-06 15:00:00+00

Rextester Demo

将逻辑事件分组

1 个答案: