Question

我如何优化查询，它已经花了大约2秒，在'结果'表中有大约500k的记录，但我希望这个数字增长到数十亿。

 SELECT
     hopcount, hop, round( avg( rtt ) , 2 ) AS avg, min( rtt ) AS min, max( rtt ) AS        max
FROM results
JOIN traces ON id = trace
WHERE target =9
AND rtt > -1
GROUP BY hop`

解释输出：

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra   
1   SIMPLE  traces  ref PRIMARY,fk_traces_1_idx fk_traces_1_idx 5   const   26333   Using where; Using temporary; Using filesort  
1   SIMPLE  results ref trace   trace   5   pinger.traces.id    7   Using where

表格：

CREATE TABLE IF NOT EXISTS `results` (
  `hop` int(11) DEFAULT NULL,
  `trace` int(11) DEFAULT NULL,
  `rtt` int(11) NOT NULL,
  `seq` int(11) NOT NULL,
  KEY `trace` (`trace`),
  KEY `fk_hops_id` (`hop`),
  KEY `seq` (`seq`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;  
    CREATE TABLE IF NOT EXISTS `traces` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `hopcount` smallint(6) NOT NULL,
  `target` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fk_traces_1_idx` (`target`,`id`,`time`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=52308;

Answer 1

在MySQL中，GROUP BY暗示ORDER BY

要删除此隐式排序，请添加ORDER BY NULL

MySQL docs for SELECT

中提到了这一点

如果使用GROUP BY，则输出行将根据GROUP BY列进行排序，就好像您具有相同列的ORDER BY一样。为了避免GROUP BY产生的排序开销，添加ORDER BY NULL：

还有ORDER BY Optimization

MySQL使用filesort缓慢平均最大最大值

1 个答案: