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Coding Tree
提交 302b9f94 编写于 作者: 彭世瑜's avatar 彭世瑜
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blog/mysq-advance/index.md
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......@@ -34,7 +34,4 @@ MySQL 运维篇
- [https://www.yuque.com/heychu/akbndd/zhuxqd](https://www.yuque.com/heychu/akbndd/zhuxqd)
https://www.bilibili.com/video/BV1Kr4y1i7ru?p=71&spm_id_from=pageDriver
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https://www.bilibili.com/video/BV1Kr4y1i7ru?p=75&spm_id_from=pageDriver
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blog/mysq-advance/mysql-index.md
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......@@ -110,6 +110,249 @@ Hash索引的特点:
InnoDB中具有自适应hash功能
### 2.7、思考
为什么InnoDB存储引擎选择使用B+Tree索引结构？
1. 相对于二叉树，层级更少，搜索效率高
2. 相对于B-Tree，无论是叶子节点还是非叶子节点，都会保存数据，这样导致一页中存储的键值减少，指针减少，要保存同样的数据量，只能增加树的高度，导致性能降低
3. 相对于Hash索引，B+Tree支持范围匹配及排序操作
## 3、索引分类
|分类 | 含义 | 特点 | 关键字|
|-|-|-|-|
|主键索引 | 针对于表中主键创建的索引|默认自动创建，只能有一个 | primary |
|唯一索引 | 避免同一个表中某列数据中的值重复 | 可以有多个 | unique |
|常规索引|快读定位特定数据 | 可以有多个| index |
|全文索引 |全文索引查找的是文本中的关键词，而不是比较索引中的值 | 可以有多个| fulltext |
根据索引存储形式，又可以分为
|分类 | 含义 | 特点|
|-|-|-|
| 聚集索引 clustered index | 将数据存储与索引放到了一块，索引结构的叶子节点保存了行数据 | 必须有，而且只有一个 |
| 二级索引 secondary index | 将数据与索引分开存储，索引结构的叶子节点关联的是对应的主键 | 可以存在多个 |
聚集索引选取规则：
1. 如果存在主键，主键索引就是聚集索引
2. 如果不存在主键，将使用第一个唯一索引（unique）作为聚集索引
3. 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
索引示例
![](img/cluster-index.png)
查询示例
![](img/index-return.png)
### 3.1、思考1
以下SQL语句，哪个执行效率高？为什么？
```sql
select * from user where id = 10;
select * from user where name = 'Arm';
```
备注：id为主键，name字段有索引
直接用id查询效率较高
1. id查询可以使用聚集索引
2. name查询需要使用回表查询，先查询二级索引，查询到id，再查询聚集索引
### 3.2、思考2
InnoDB主键索引的B+Tree高度为多高？
假设：
一页中可以存储16k数据，一行数据大小为1k，可以存储16行。InnoDB的指针占用6个字节，主键即使为bigint，占用字节数为8。
树的高度为2：
```js
// n为key的数量 (n+1)表示指针数量
n * 8 + ( n + 1) * 6 = 16 * 1024 // 算出n约等于1170
1171 * 16 = 18736
```
如果高度为3
```js
1171 * 1171 * 16 = 21939856
```
## 4、索引的语法
创建索引
```sql
create [unique|fulltext] index index_name on table_name (index_column_name,...);
```
查看索引
```sql
show index form table_name;
```
删除索引
```sql
drop index index_name on table_name;
```
### 4.1、案例
需求：
1. name姓名字段，该字段的值可能会重复，该字段创建索引
2. phone手机号字段，是非空，且唯一的，创建唯一索引
3. 为profession、age、status创建联合索引
4. 为email建立合适的索引来提升查询效率
准备测试数据
```sql
create table tb_user(
id int primary key auto_increment comment '主键',
name varchar(20) comment '姓名',
phone varchar(11) comment '手机号',
profession varchar(10) comment '专业',
age int comment '年龄',
status int comment '状态',
email varchar(50) comment '邮箱'
);
-- 插入测试数据
insert into tb_user (name, phone, profession, age, status, email)
values ('张飞', '15210231227', '美术', 23, 1, '123@qq.com');
insert into tb_user (name, phone, profession, age, status, email)
values ('关羽', '15210231297', '物理', 24, 1, '3339@qq.com');
insert into tb_user (name, phone, profession, age, status, email)
values ('刘备', '15214231297', '数学', 25, 0, '666@qq.com');
insert into tb_user (name, phone, profession, age, status, email)
values ('孙权', '15215231297', '语文', 20, 1, '111@qq.com');
-- 查看数据
mysql> select * from tb_user;
+----+--------+-------------+------------+------+--------+-------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+-------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 2 | 关羽 | 15210231297 | 物理 | 24 | 1 | 3339@qq.com |
| 3 | 刘备 | 15214231297 | 数学 | 25 | 0 | 666@qq.com |
| 4 | 孙权 | 15215231297 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+-------------+
4 rows in set (0.00 sec)
-- 查看已有索引
mysql> show index from tb_user;
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
1 row in set (0.01 sec)
-- 或者
mysql> show index from tb_user\G
*************************** 1. row ***************************
Table: tb_user
Non_unique: 0
Key_name: PRIMARY
Seq_in_index: 1
Column_name: id
Collation: A
Cardinality: 4
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
Visible: YES
Expression: NULL
1 row in set (0.00 sec)
```
完成需求
```sql
-- 创建普通索引
create index idx_user_name on tb_user (name);
-- 默认创建B+Tree的索引结构
show index from tb_user;
+---------+------------+---------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+---------+------------+---------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+---------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
2 rows in set (0.00 sec)
-- 创建唯一索引
create unique index idx_user_phone on tb_user (phone);
mysql> show index from tb_user;
+---------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+---------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
3 rows in set (0.01 sec)
-- 创建联合索引
create index idx_user_profession_age_status on tb_user (profession, age, status);
mysql> show index from tb_user;
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
6 rows in set (0.00 sec)
-- 创建普通索引
create index idx_user_email on tb_user (email);
mysql> show index from tb_user;
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
| tb_user | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_email | 1 | email | A | 4 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
7 rows in set (0.00 sec)
```
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