WebFilesort: Scan the table to be sorted and collect the sort keys in a temporary file. Sort the keys + reference to row (with filesort) Scan the table in sorted order Use a temporary table for ORDER BY : Create a temporary (in memory) table for the 'to-be-sorted' data. WebApr 11, 2024 · 4、排序(order by)优化 在 mysql,排序主要有两种方式 Using filesort : 通过表索引或全表扫描,读取满足条件的数据行,然后在排序缓冲区 sort。 buffer 中完成排序操作,所有不是通过索引直接返回排序结果的排序都叫 FileSort 排序; Using index : 通过有序的索引顺序扫描直接返回有序数据,这种情况即为 using index,不需要额外排序,操作 …
MySQL ORDER BY / LIMIT performance: late row lookups
WebDec 3, 2010 · Id & timestamp is a primary key pair (mediumint+datetime) dataTypeId is a foreign key (mediumint) table is created as InnoDb. There can be more records with same … WebMar 5, 2009 · Extra: Using filesort 1 row in set (0.00 sec) mysql> ALTER TABLE t1 ADD INDEX (id); Query OK, 2 rows affected (0.03 sec) Records: 2 Duplicates: 0 Warnings: 0. … flx bandit
Order Byを制して一覧表示を速くする - Qiita
WebSep 30, 2013 · 2. If it's reasonable to re-write your query as a join: select e.* from emp e inner join department d on e.id = d.order where d.name = 'testing' order by d.order asc. Where this would change your results is if there are multiple rows in department with the same order value matching one or more rows in emp - in which case this query will return ... WebApr 13, 2024 · select * from history order by id MySQL 会直接遍历上图 id 索引的叶子节点链表,不需要进行额外的排序操作。 这就是用索引扫描来排序。 ②使用文件排序 (filesort) 但如果 id 字段没有任何索引,上图的 B+Tree 结构不存在,MySQL 就只能先扫表筛选出符合条件的数据,再将筛选结果根据 id 排序。 这个排序过程就是 filesort。 我们要让 ORDER BY … It will use the index and do no filesort because the query needs only the values that are stored in the index. If you want a similar (to InnoDB) behaviour in MyiSAM, you coud try creating an index on (comment_id, comment_content, comment_author, comment_author_url) and then try your query. flxbasic