MySQL的：有效地轉化事件日誌，以時間序列

Question

我有一個表記錄的開始時間和感興趣的事件的結束時間：

CREATE TABLE event_log (start_time DATETIME, end_time DATETIME); 
INSERT INTO event_log VALUES ("2013-06-03 09:00:00","2013-06-03 09:00:05"), ("2013-06-03 09:00:03","2013-06-03 09:00:07"), ("2013-06-03 09:00:10","2013-06-03 09:00:12"); 

+---------------------+---------------------+ 
| start_time   | end_time   | 
+---------------------+---------------------+ 
| 2013-06-03 09:00:00 | 2013-06-03 09:00:05 | 
| 2013-06-03 09:00:03 | 2013-06-03 09:00:07 | 
| 2013-06-03 09:00:10 | 2013-06-03 09:00:12 | 
+---------------------+---------------------+ 

我正在尋找一種方式來創建一個「時間序列」表，其中一列是時間索引，另一列是當時正在進行的事件的計數。我可以通過子查詢和生成器來完成：

SET @first_time := (SELECT MIN(start_time) FROM event_log); 
SET @last_time := (SELECT MAX(end_time) FROM event_log); 

CREATE OR REPLACE VIEW generator_16 
AS SELECT 0 n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL 
    SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL 
    SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL 
    SELECT 9 UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL 
    SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL 
    SELECT 15; 

CREATE TABLE time_series (t DATETIME, event_count INT(11)) 
SELECT @first_time + INTERVAL n SECOND t, NULL AS event_count 
    FROM generator_16 
    WHERE @first_time + INTERVAL n SECOND <= @last_time; 

UPDATE time_series 
    SET event_count= (SELECT COUNT(*) FROM event_log 
    WHERE start_time<=t AND end_time>=t); 

+---------------------+-------------+ 
| t     | event_count | 
+---------------------+-------------+ 
| 2013-06-03 09:00:00 |   1 | 
| 2013-06-03 09:00:01 |   1 | 
| 2013-06-03 09:00:02 |   1 | 
| 2013-06-03 09:00:03 |   2 | 
| 2013-06-03 09:00:04 |   2 | 
| 2013-06-03 09:00:05 |   2 | 
| 2013-06-03 09:00:06 |   1 | 
| 2013-06-03 09:00:07 |   1 | 
| 2013-06-03 09:00:08 |   0 | 
| 2013-06-03 09:00:09 |   0 | 
| 2013-06-03 09:00:10 |   1 | 
| 2013-06-03 09:00:11 |   1 | 
| 2013-06-03 09:00:12 |   1 | 
+---------------------+-------------+ 

有沒有更高效的方法來做到這一點？這種方法每次索引都需要一個子查詢。例如，是否有一種方法可以實現，即每個「event_log」記錄需要一個子查詢？我真正的問題是500k時間索引條目和1k事件;它需要比我想要的時間長一些（大約90秒）。

「發電機」片段來自http://use-the-index-luke.com/blog/2011-07-30/mysql-row-generator。顯然，較大的發生器之一，如64k版本或1M版本，將需要更大的問題。

Answer 1

唯一的變化發生在start_time和end_time。 所以，如果你是

select distinct start_time As time_point from event_log 
UNION 
select distinct end_time As time_point from event_log 

...這將讓你在你需要的快照所有的「點」。

如果您在臨時表（如TEMP_POINTS）中創建該參數，並且如果返回event_log，則應該可以計算每個「點」處的事件數。

CREATE TABLE NON_ZERO_POINTS (t DATETIME, event_count INT(11)) 
    select time_point, count(*) 
    from TEMP_POINTS 
    join event_log on time_point between start_time and end_time 
    group by time_point 

可能是值得創建於NON_ZERO_POINTS

然後索引，你可以在你的更新從而使用NON_ZERO_POINTS：

UPDATE time_series 
SET event_count= (SELECT event_count FROM NON_ZERO_POINTS 
WHERE t=time_point); 

另外，你需要更新time_series？如果不是，則可以在查詢中使用它：

select t, coalesce(event_count) 
from time_series 
left join FROM NON_ZERO_POINTS 
on t=time_point