re_mysql_20221212【进阶1：存储引擎与索引】

files/hm-mysql/MySQL-2-advance.pdf · yppah/apibooks - 码云 - 开源中国 (gitee.com)

1. 存储引擎

1.1 mysql结构体系

连接层：处理客户端连接，授权认证校验权限等操作
服务层：核心，sql接口、sql解析、sql优化等所有跨存储引擎的操作
引擎层：索引；不同存储引擎的索引结构不同
存储层：数据索引&日志等存储在磁盘文件中

1.2 存储引擎

1.3 存储引擎特点

1.3.1 InnoDB

1.3.2 MyISAM

1.3.3 Memory

1.4 区别&怎么选

目前

mysql默认InnoDB，不常用MyISAM和MEMORY

在需要使用MyISAM这种场景时，往往选择nosql数据库mongoDB

在需要使用MEMORY这种场景时，往往选择nosql数据库redis

2. 索引

MySQL 索引 | xustudyxu's Blog (frxcat.fun)

2.1 概述

2.2 索引结构 (重点：B+树；了解：Hash)

2.2.1 二叉树

2.2.2 B树

2.2.3 B+树

2.2.4 Hash

结构

哈希索引就是采用一定的hash算法，将键值换算成新的hash值，映射到对应的槽位上，然后存储在hash表中。

特点

Hash索引只能用于对等比较(=，in)，不支持范围查询（between，>，< ，...）
无法利用索引完成排序操作
查询效率高，通常(不存在hash冲突的情况)只需要一次检索就可以了，效率通常要高于B+tree索引

存储引擎支持

在MySQL中，支持hash索引的是Memory存储引擎。而InnoDB中具有自适应hash功能，hash索引是InnoDB存储引擎根据B+Tree索引在指定条件下自动构建的。

2.3 索引分类

分类1

分类2

聚集索引选取规则：

如果存在主键，主键索引就是聚集索引。
如果不存在主键，将使用第一个唯一（UNIQUE）索引作为聚集索引。
如果表没有主键，或没有合适的唯一索引，则InnoDB会自动生成一个rowid作为隐藏的聚集索引。

2.4 索引语法

create table tb_user(
	id int primary key auto_increment comment '主键',
	name varchar(50) not null comment '用户名',
	phone varchar(11) not null comment '手机号',
	email varchar(100) comment '邮箱',
	profession varchar(11) comment '专业',
	age tinyint unsigned comment '年龄',
	gender char(1) comment '性别 , 1: 男, 2: 女',
	status char(1) comment '状态',
	createtime datetime comment '创建时间'
) comment '系统用户表';


INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('吕布', '17799990000', 'lvbu666@163.com', '软件工程', 23, '1', '6', '2001-02-02 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('曹操', '17799990001', 'caocao666@qq.com', '通讯工程', 33, '1', '0', '2001-03-05 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('赵云', '17799990002', '17799990@139.com', '英语', 34, '1', '2', '2002-03-02 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('孙悟空', '17799990003', '17799990@sina.com', '工程造价', 54, '1', '0', '2001-07-02 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('花木兰', '17799990004', '19980729@sina.com', '软件工程', 23, '2', '1', '2001-04-22 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('大乔', '17799990005', 'daqiao666@sina.com', '舞蹈', 22, '2', '0', '2001-02-07 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('露娜', '17799990006', 'luna_love@sina.com', '应用数学', 24, '2', '0', '2001-02-08 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('程咬金', '17799990007', 'chengyaojin@163.com', '化工', 38, '1', '5', '2001-05-23 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('项羽', '17799990008', 'xiaoyu666@qq.com', '金属材料', 43, '1', '0', '2001-09-18 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('白起', '17799990009', 'baiqi666@sina.com', '机械工程及其自动化', 27, '1', '2', '2001-08-16 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('韩信', '17799990010', 'hanxin520@163.com', '无机非金属材料工程', 27, '1', '0', '2001-06-12 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('荆轲', '17799990011', 'jingke123@163.com', '会计', 29, '1', '0', '2001-05-11 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('兰陵王', '17799990012', 'lanlinwang666@126.com', '工程造价', 44, '1', '1', '2001-04-09 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('狂铁', '17799990013', 'kuangtie@sina.com', '应用数学', 43, '1', '2', '2001-04-10 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('貂蝉', '17799990014', '84958948374@qq.com', '软件工程', 40, '2', '3', '2001-02-12 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('妲己', '17799990015', '2783238293@qq.com', '软件工程', 31, '2', '0', '2001-01-30 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('芈月', '17799990016', 'xiaomin2001@sina.com', '工业经济', 35, '2', '0', '2000-05-03 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('嬴政', '17799990017', '8839434342@qq.com', '化工', 38, '1', '1', '2001-08-08 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('狄仁杰', '17799990018', 'jujiamlm8166@163.com', '国际贸易', 30, '1', '0', '2007-03-12 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('安琪拉', '17799990019', 'jdodm1h@126.com', '城市规划', 51, '2', '0', '2001-08-15 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('典韦', '17799990020', 'ycaunanjian@163.com', '城市规划', 52, '1', '2', '2000-04-12 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('廉颇', '17799990021', 'lianpo321@126.com', '土木工程', 19, '1', '3', '2002-07-18 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('后羿', '17799990022', 'altycj2000@139.com', '城市园林', 20, '1', '0', '2002-03-10 00:00:00');
INSERT INTO itcast.tb_user (name, phone, email, profession, age, gender, status, createtime) VALUES ('姜子牙', '17799990023', '37483844@qq.com', '工程造价', 29, '1', '4', '2003-05-26 00:00:00');

show index from tb_user;

# 1. name字段为姓名字段，该字段的值可能会重复，为该字段创建索引
create index idx_user_name on tb_user(name);
show index from tb_user;

# 2. phone手机号字段的值，是非空，且唯一的，为该字段创建唯一索引
create unique index idx_user_phone on tb_user(phone);
show index from tb_user;

# 3. 为profession、age、status创建联合索引
create index idx_user_pro_age_sta on tb_user(profession, age, status);
show index from tb_user;

# 4. 为email建立合适的索引来提升查询效率
create index idx_user_email on tb_user(email);
show index from tb_user;