Java structure for set of sets that have to union? (for Kruskal's Algorithm) I have to implement Kruskal's Algorithm in Java. I have the part that I get the edges ordered by weight, but I am a little lost when I
基于Mysql5.7版本的explain参数详解… mysql官网相关参数解读 一:id SELECT标识符 1.id越大越先执行 2.相同id,从从往下执行 二:select_type 1.SIMPLE :最简单的查询(没有关联查询没有子查询没有union的查询语句) 2:PRIMARY:子查询最外层的查询语句 3.SUBQUERY:子查询内层查询语句 4.DERIVED:派生表查... ...
/* Navicat Premium Data Transfer Source Server : localhost Source Server Type : MySQL Source Server Version : 50739 (5.7.39) Source Host : localhost:3306 Source Schema : cheetah Target Server Type : MySQL Target Server Version : 50739 (5.7.39) File Encoding : 65001 Date: 12/11/2022 18:...
4)eq_ref:多表连接中使用primary key或者 unique key作为关联条件,使用唯一性索引进行数据查找,也就是被关联表上的关联列走的是主键或者唯一索引这可能是在const之外最好的联接类型了,简单的select查询不会出现这种type 5)ref:使用了非唯一性索引进行数据的查找或者非唯一性索引的部分前缀 5.1)简单查询(非唯一索引)...
pfree(es->str->data);}/* * Create a new ExplainState struct initialized with default options. */ExplainState *NewExplainState(void){ ExplainState *es = (ExplainState *) palloc0(sizeof(ExplainState)); /* Set default options (most fields can be left as zeroes). */ es->costs = true...
1.2 select_type MySQL将SELECT查询分为简单查询SIMPLE和复杂查询PRIMARY。复杂查询包括:简单子查询、派生表( FROM 语句中的子查询)、UNION 和 UNION ALL 查询。 1、SUBQUERY 在SELECT或WHERE中包含了子查询,例如: EXPLAINSELECT(SELECT1FROMstudent LIMIT1)FROMstudent; ...
DROP database IF EXISTS `explain_test`; create database `explain_test` DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci; -- switch database use `explain_test`; -- --- -- table structure for `tb_book` -- --- DROP TABLE IF EXISTS `tb_...
type: const possible_keys: PRIMARY key: PRIMARY key_len: 4 ref: const rows: 1 filtered: 100.00 Extra: NULL *** 总的来说,explain 关键字可以告诉我们下面这么多信息: 表的读取顺序如何 数据读取操作有哪些操作类型 哪些索引可以使用 哪些索引被实际使用...
These formats share a common logic that uses AccessPath structure to generate the information, so they all display exactly the same information, even though the style of each format might be different. Note : The new json format for hypergraph and the tree format are examples of iterator-based...
type: const possible_keys: PRIMARY key: PRIMARY key_len: 4 ref: const rows: 1 filtered: 100.00 Extra: NULL *** 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 总的来说,explain 关键字可以告诉我们下面这么多信息:...