WebApr 12, 2024 · 如果不可避免出现filesort,大数据量排序,可以适当增大排序缓冲区大小,参数sort_buffer_size(默认256K) group by优化. 也需要满足最左前缀法则. limit优化. 越往后效率越低. 可以通过覆盖索引和子查询优化. count优化 WebApr 12, 2024 · 引用视频里的话: using Filesort:(九死一生)、 Using temporary:(十死无生)还有distinct 总之这几个能不用就不用,尽量去优化. 然后就开始了修改sql语句之旅。 …
mysql查询过程优化--理论及实践过程总结 - Monster1728 - 博客园
WebAug 9, 2024 · What catches my eye with your sample query is "there is no WHERE clause". That being the case, the query is basically doing a full join. Even if authorFK is indexed in the titles table, the MySQL query optimizer decided that doing Using temporary; Using filesort is better than trying to use the index in the join process. If your real query features Using … WebIf an index cannot be used to satisfy an ORDER BY clause, MySQL performs a filesort operation that reads table rows and sorts them. A filesort constitutes an extra sorting phase in query execution.. To obtain memory for filesort operations, as of MySQL 8.0.12, the optimizer allocates memory buffers incrementally as needed, up to the size indicated by … chips ahoy jokes
MySQL查询优化:GROUP BY - ppjj - 博客园
WebNov 25, 2024 · extra列,详细说明。注意常见的不太友好的值有:Using filesort, Using temporary; 二、SQL语句中IN包含的值不应过多. MySQL对于IN做了相应的优化,即将IN中的常量全部存储在一个数组里面,而且这个数组是排好序的。但是如果数值较多,产生的消耗也 … Web我们可以看到三种强制的预期,. 1 我们的group by 或 distinct 操作的数据结果集是比较大的,则使用big_result,MYSQL会在磁盘创建临时表,并且很可能走全表扫描的方式. 2 如果 … Web8.2.1.19 LIMIT Query Optimization. If you need only a specified number of rows from a result set, use a LIMIT clause in the query, rather than fetching the whole result set and throwing away the extra data. MySQL sometimes optimizes a query that has a LIMIT row_count clause and no HAVING clause: grapevine fireworks 2021