2

我有一个事件表，其中包含大约 100k 行。以下是对“事件”表的复杂查询，希望对如何优化此查询提出您的意见...

SELECT id FROM event 
NATURAL JOIN (
    SELECT subj_id, max(timestamp) AS timestamp
    FROM event WHERE (
        timestamp >= 1342052128597 AND timestamp <= 9223372036854775807
        AND NOT subj_interpretation = 46))
    GROUP BY subj_id)
GROUP BY subj_id
ORDER BY  
timestamp DESC

查询在 0.06-0.07 秒内执行。任何想法有什么好的指标和/或查询的重组。

目前我正在使用：

CREATE INDEX event_subj_id ON event(subj_id, timestamp, subj_interpretation)

查询计划如下所示：

1 0 0 SCAN TABLE event USING COVERING INDEX event_subj_id (~27777 rows)
0 0 1 SCAN SUBQUERY 1 (~100 rows)
0 1 0 SEARCH TABLE event USING INDEX event_subj_id (subj_id=? AND timestamp=?) (~9 rows)
0 0 0 USE TEMP B-TREE FOR GROUP BY
0 0 0 USE TEMP B-TREE FOR ORDER BY
4

1 回答 1

1

您可以通过删除来优化您的第二个查询DISTINCT，因为GROUP BY subj_id已经确保不能有重复的记录：

SELECT id,
       subj_id,
       max(timestamp) AS timestamp
FROM event
WHERE timestamp BETWEEN 1342055894621 AND 9223372036854775807
  AND subj_interpretation != 46
GROUP BY subj_id
ORDER BY timestamp

索引本身已经是最佳的GROUP BY//查找timestamp。subj_interpretation但是，如果将id列添加到其中，SQLite 可以将其用作覆盖索引，这样就无需在events表本身中查找任何记录，这实际上可能使性能翻倍：

0 0 0 SCAN TABLE event USING COVERING INDEX event_subj_id_plus_id
0 0 0 USE TEMP B-TREE FOR ORDER BY
于 2013-01-04T13:22:05.010 回答