SQL：很少有時間差

Question

選擇行我有一個表

event_id eventtypeid eventtimestamp

描述，可以是相互接近時的事件。我想查找事件對，其中事件類型相同，時間戳之間的差異不超過3毫秒。

在sql中一般可能嗎？我如何制定這樣的要求？

預先感謝您。

Answer 1

SELECT 
    * 
FROM 
    event_table AS first 
INNER JOIN 
    event_table AS second 
    ON second.eventtypeid  = first.eventtypeid 
    AND second.eventtimestamp > first.eventtimestamp 
    AND second.eventtimestamp <= first.eventtimestamp + INTERVAL '3 milliseconds' 

Answer 2

查詢像這些一般最好用window function解決：

SELECT eventtypeid, first, second, diff 
FROM (
    SELECT eventtypeid, event_id AS first, lead(event_id) OVER w AS second, 
     lead(eventtimestamp) OVER w - eventtimestamp AS diff 
    FROM event_table 
    WINDOW w AS (PARTITION BY eventtypeid ORDER BY eventtimestamp) 
) sub 
WHERE diff <= interval '3 milliseconds'; 

這通常比自聯接快得多。