explain explain用来查看执行计划,使用explain关键字可以模拟优化器执行SQL查询语句,从而知道mysql是如何处理你的SQL语句,分析你的查询语句或是表结构的性能瓶颈 可以获得如下信息 表的读取顺序 数据读取操作的操作类型 哪些索引可以使用 哪些索引被实际使用 表之间的引用 每张表有多少行被优化器查询 如何使用 explain + ...
EXPLAIN可以模拟优化器执行SQL查询语句,从而指导MySQL是如何处理你的SQL语句的。可用来分析查询语句或表结构的性能瓶颈。可以查看: 表的读取顺序 数据读取操作的操作类型哪些索引可以... 3,5type:查询使用类型system>const>eq_ref>ref>range>index>allpossible_keys ...
One of the most painful tasks isto analyze and optimize a Stored Procedure because MySQL does not log the individualqueriesfrom a Procedureand ’s hard to actually see what is going under the hood”. Since MySQL 5.7 you can trace SP, look at WL#5766 (https://dev.mysql.com/worklog/...
Tutorial: Using Explain to Improve Query Performance Database Development Database Design and Modeling Database Migration Wizard MySQL Workbench Frequently Asked Questions Keyboard Shortcuts Extending Workbench How To Report Bugs or Problems MySQL Enterprise Features MySQL Utilities Related...
mysql无法使用其前缀索引做ORDER BY和GROUP BY,也无法使用前缀索引做覆盖扫描。 联合索引 如何选择索引列的顺序 经常会被使用到的列优先,放到联合索引的最左边 。 但也不是绝对的,举个例子 有个状态 state,就几个值, 选择性很差(因为根据每个state,筛选出来的数据太多了。。。)就不适合放到联合索引的最左边 ...
Number in top left of a box: relative cost of accessing that table (requires MySQL 5.7 or higher) Number to the right of nested loop (or hash join) diamonds: number of rows produced by the JOIN Number above the diamonds: relative cost of the JOIN (requires MySQL 5.7 or higher) ...
显示关于可能用到的命令的信息,它是mysql里面最有用的一个命令,有了它就不用担心记不清语法了。 基本语法: HELP 'search_string' 实例: mysql> HELP 'contents'You asked for help about help category: "Contents"For more information, type 'help <item>', where <item> is one of the followingcategori...
Features Resources What's New Editions Support Download Buy Now MySQL EXPLAIN: Analyze MySQL Queries With the EXPLAIN Plan MySQL EXPLAIN plan, also known as execution plan, helps you understand how MySQL queries are executed and what indexing techniques are better for running queries efficie...
Oracle:For Oracle, to perform an explain plan, the PLAN_TABLE must exist. For example, CREATE PUBLIC SYNONYM plan_table FOR sys.plan_table; GRANT ALL ON sys.plan_table TO public; For the rest of the databases supported by the explain plan tool - HSQLDB, MySQL, PostgreSQL, SQLite, SQL ...
Description: EXPLAIN FORMAT=JSON can print additional value if compare to regular EXPLAIN, such as query cost, but these features are not documented anywhere How to repeat: mysql> EXPLAIN FORMAT=JSON SELECT user, host FROM mysql.user\G *** 1. row *** EXPLAIN { "query_block": { "select...