diff --git a/blog/mysq-advance/img/cluster-index.png b/blog/mysq-advance/img/cluster-index.png new file mode 100644 index 0000000000000000000000000000000000000000..6ee189a9425eb5ac3c2c52585baa01071377c536 Binary files /dev/null and b/blog/mysq-advance/img/cluster-index.png differ diff --git a/blog/mysq-advance/img/index-return.png b/blog/mysq-advance/img/index-return.png new file mode 100644 index 0000000000000000000000000000000000000000..8b94537e9955c8fb7bb47b27ad6beb6060aa3c12 Binary files /dev/null and b/blog/mysq-advance/img/index-return.png differ diff --git a/blog/mysq-advance/index.md b/blog/mysq-advance/index.md index 7eb81d29b54ade4637f35268b0b12294ebdaa423..4556549f44529d8be5078ed1d6d920338a3c7abf 100644 --- a/blog/mysq-advance/index.md +++ b/blog/mysq-advance/index.md @@ -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 \ No newline at end of file +https://www.bilibili.com/video/BV1Kr4y1i7ru?p=75&spm_id_from=pageDriver \ No newline at end of file diff --git a/blog/mysq-advance/mysql-index.md b/blog/mysq-advance/mysql-index.md index 8de9b9461fc1ce7577f78cbc94e7ac6985ef4209..c2ee3908a526075177f16d034e65d756bafb55a5 100644 --- a/blog/mysq-advance/mysql-index.md +++ b/blog/mysq-advance/mysql-index.md @@ -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) +``` \ No newline at end of file