EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joins using a nested-loop join method. Thismeans that MySQL reads a row from the first ...
DELIMITER //CREATEPROCEDUREinsert_s1 (INmin_numINT(10),INmax_numINT(10))BEGINDECLAREiINTDEFAULT0;SETautocommit =0;REPEATSETi = i +1;INSERTINTOs1VALUES((min_num + i),rand_string(6),(min_num +30* i +5),rand_string(6),rand_string(10),rand_string(5),rand_string(10),rand_string(...
https://dev.mysql.com/doc/workbench/en/wb-performance-explain.html 标准框--红色:全表扫描(花费极高),全索引扫描(花费高) 圆脚框--group/sort,分组或排序 钻石框--joins Framed boxes(有外框)--子查询。 Join type连接类型: https://dev.mysql.com/doc/refman/8.0/en/explain-output.html#explain-joi...
{ "transformations_to_nested_joins": { "transformations": [ "parenthesis_removal" ] /* transformations */, "expanded_query": "/* select#2 */ select group_concat(`f`.`title` order by `f`.`title` ASC separator ', ') from `film` `f` join `film_category` `fc` join `film_actor`...
Diamonds: joins Textual and Informational Conventions Standard text below boxes: table (or alias) name Bold text below boxes: key/index that was used Number in top right of a box: number of rows used from the table after filtering Number in top left of a box: relative cost of accessing ...
Bug #113303Explain plan takes forever when there are more joins Submitted:1 Dec 2023 7:29Modified:1 Dec 2023 7:44 Reporter:Yunus ShaikhEmail Updates: Status:VerifiedImpact on me: None Category:MySQL Server: OptimizerSeverity:S5 (Performance) ...
migrate-large-mysql-to-tidb.md migrate-small-mysql-shards-to-tidb.md migrate-small-mysql-to-tidb.md migrate-with-more-columns-downstream.md migrate-with-pt-ghost.md migration-overview.md migration-tools.md minimal-deployment-topology.md multi-data-centers-in-one-city-deployment.md mysql-compa...
EXPLAIN作为MySQL的性能分析神器,读懂其结果是很有必要的,然而我在各种搜索引擎上竟然找不到特别完整的解读。都是只有重点,没有细节(例如type的取值不全、Extra缺乏完整的介绍等)。 所以,我肝了将近一个星期,整理了一下。这应该是全网最全面、最细致的EXPLAIN解读文章了,下面是全文。
这个算法与 MySQL 主要使用的 Join 算法类似。在下表的示例中,TableReader_29(Build) 算子首先读取表 t1,然后根据在 t1 中匹配到的每行数据,依次探查表 t2 中的数据: 注意 在执行计划返回结果中,自 v6.4.0 版本起,特定算子(即 IndexJoin 和Apply 算子的 Probe 端所有子节点)的 estRows 字段意义与 v6.4....
Index columns used in JOINs and foreign keys.These are common scenarios where indexing can significantly enhance query performance. Additional Considerations Types of Indexes.MySQL supports various types of indexes such as primary, unique, full-text, and spatial indexes. Understanding these can help in...