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提交 3d332568 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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...@@ -34,4 +34,4 @@ MySQL 运维篇 ...@@ -34,4 +34,4 @@ MySQL 运维篇
- 3. [https://www.yuque.com/heychu/akbndd/zhuxqd](https://www.yuque.com/heychu/akbndd/zhuxqd) - 3. [https://www.yuque.com/heychu/akbndd/zhuxqd](https://www.yuque.com/heychu/akbndd/zhuxqd)
https://www.bilibili.com/video/BV1Kr4y1i7ru?p=84&spm_id_from=pageDriver https://www.bilibili.com/video/BV1Kr4y1i7ru?p=86&spm_id_from=pageDriver
\ No newline at end of file \ No newline at end of file
blog/mysq-advance/mysql-index.md
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...@@ -1124,38 +1124,487 @@ explain select * from tb_user where age = 23 and status = 1 and profession = ' ...@@ -1124,38 +1124,487 @@ explain select * from tb_user where age = 23 and status = 1 and profession = '
1 row in set, 1 warning (0.00 sec) 1 row in set, 1 warning (0.00 sec)
``` ```
### 6.3、范围查询 ### 6.3、SQL提示
联合索引中，出现范围查询（>、<），范围查询右侧的列索引失效 SQL提示是优化数据库的一个重要手段
简单来说，就是在SQL语句中加入一些认为的提示来达到优化操作的目的
```sql
-- 1、use index 推荐使用索引
explain select * from tb_user use index (idx_user_profession) where profession = '法务经理';
-- 2、ignore index 忽略使用索引
explain select * from tb_user ignore index (idx_user_profession) where profession = '法务经理';
-- 3、force index 强制使用索引
explain select * from tb_user force index (idx_user_profession) where profession = '法务经理';
```
测试数据准备
```sql
drop table if exists tb_user;
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(50) comment '专业',
age int comment '年龄',
status int comment '状态',
email varchar(50) comment '邮箱'
);
```
利用Python脚本生成10万条测试数据
```python
# 安装依赖 pip install faker records mysqlclient
from faker import Faker
import records
# 简体中文：zh_CN
faker = Faker(locale="zh_CN")
# 指定随机种子，确保每次生成的数据都是一致的
faker.seed(1)
# 生成数据插入 insert sql
def get_insert_sql(table_name, fields):
keys = ', '.join([f'`{key}`'.format(key) for key in fields])
values = ', '.join([f':{key}'.format(key) for key in fields])
return f'INSERT INTO `{table_name}` ({keys}) VALUES ({values})'
# 获取数据
def get_row():
return {
'name': faker.name(),
'phone': faker.phone_number(),
'email': faker.email(),
'age': faker.random_int(20, 30),
'status': faker.random_int(0, 1),
'profession': faker.job(),
}
def main():
db = records.Database('mysql://root:123456@localhost/data?charset=utf8')
# 10 * 1000 = 1万条数据
for i in range(10):
data = [get_row() for _ in range(1000)]
sql = get_insert_sql('tb_user', data[0].keys())
db.bulk_query(sql, data)
if __name__ == '__main__':
main()
```
查看生成的测试数据
```sql
mysql> select count(*) from tb_user;
+----------+
| count(*) |
+----------+
| 10000 |
+----------+
select * from tb_user limit 10;
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
| id | name | phone | profession | age | status | email |
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
| 1 | 费阳 | 13777763170 | 法务经理 | 27 | 1 | wyao@gmail.com |
| 2 | 祁海燕 | 13400806360 | 日式厨师 | 23 | 0 | jwan@jin.cn |
| 3 | 姬秀英 | 18281241586 | 食品/饮料研发 | 29 | 0 | li97@wang.cn |
| 4 | 官桂芳 | 15625851781 | 前台接待/总机/接待生 | 20 | 1 | fpeng@chang.cn |
| 5 | 应秀珍 | 13030388368 | 酒店前台 | 20 | 1 | qiang48@hotmail.com |
| 6 | 亢婷 | 18207598386 | 药品市场推广主管/专员 | 28 | 1 | ping50@hotmail.com |
| 7 | 仰俊 | 13192184011 | 机场代表 | 24 | 0 | wcai@liang.net |
| 8 | 匡洁 | 13622482447 | 汽车电工 | 24 | 1 | htang@gmail.com |
| 9 | 程建华 | 13748396030 | 市场通路经理/主管 | 28 | 1 | fangguo@yahoo.com |
| 10 | 岳荣 | 15080695604 | 培训督导 | 24 | 1 | fanglong@ding.com |
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
10 rows in set (0.00 sec)
```
创建索引
```sql
-- 创建普通索引
create index idx_user_name on tb_user (name);
-- 创建唯一索引
create unique index idx_user_phone on tb_user (phone);
-- 创建联合索引
create index idx_user_profession_age_status on tb_user (profession, age, status);
-- 创建普通索引
create index idx_user_email on tb_user (email);
-- 创建索引
create index idx_user_age on tb_user ( age );
-- 查看索引
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 | 9804 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 9130 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 6232 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 7596 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_email | 1 | email | A | 9569 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_age | 1 | age | A | 11 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
8 rows in set (0.03 sec)
```
查看执行计划
```sql
mysql> explain select * from tb_user where profession = '法务经理';
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
-- 创建一个单列索引
create index idx_user_profession on tb_user (profession);
-- 性能分析
explain select * from tb_user where profession = '法务经理';
+----+-------------+---------+------------+------+----------------------------------------------------+--------------------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+----------------------------------------------------+--------------------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status,idx_user_profession | idx_user_profession_age_status | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+----------------------------------------------------+--------------------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
-- 查看执行计划（use index）使用单列索引idx_user_profession
explain select * from tb_user use index (idx_user_profession) where profession = '法务经理';
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession | idx_user_profession | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.01 sec)
-- 查看执行计划（ignore index）,忽略单列索引idx_user_profession
explain select * from tb_user ignore index (idx_user_profession) where profession = '法务经理';
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.01 sec)
-- 查看执行计划（force index）强制使用单列索引idx_user_profession
explain select * from tb_user force index (idx_user_profession) where profession = '法务经理';
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession | idx_user_profession | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
```
### 6.4、覆盖索引
查询使用了索引，并且需要返回的列，在该索引中已经全部能够找到
尽量使用覆盖索引，减少`select * `
extra额外信息：
- using index condition ： 查找使用了索引，但是需要回表查询数据（二级索引->聚集索引）
- using where; using index: 查找使用了索引，但是需要的数据都在索引列中能找到，所以不需要回表查询数据
![](img/cover-index.png)
示例
```sql
explain select id, profession from tb_user where profession = '法务经理' and age = 27 and status = 1;
explain select id, profession, age, status from tb_user where profession = '法务经理' and age = 27 and status = 1;
explain select id, profession, age, status, name from tb_user where profession = '法务经理' and age = 27 and status = 1;
explain select * from tb_user where profession = '法务经理' and age = 27 and status = 1;
```
测试
```sql
-- 查看索引
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 | 9804 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 9130 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 6232 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 7596 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_email | 1 | email | A | 9569 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_age | 1 | age | A | 11 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
9 rows in set (0.06 sec)
-- 删除多余的索引
drop index idx_user_age on tb_user;
drop index idx_user_profession on tb_user;
drop index idx_user_email on tb_user;
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 | 9804 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 9130 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 6232 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 7596 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
6 rows in set (0.00 sec)
-- 查看数据
select * from tb_user limit 10;
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
| id | name | phone | profession | age | status | email |
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
| 1 | 费阳 | 13777763170 | 法务经理 | 27 | 1 | wyao@gmail.com |
| 2 | 祁海燕 | 13400806360 | 日式厨师 | 23 | 0 | jwan@jin.cn |
| 3 | 姬秀英 | 18281241586 | 食品/饮料研发 | 29 | 0 | li97@wang.cn |
| 4 | 官桂芳 | 15625851781 | 前台接待/总机/接待生 | 20 | 1 | fpeng@chang.cn |
| 5 | 应秀珍 | 13030388368 | 酒店前台 | 20 | 1 | qiang48@hotmail.com |
| 6 | 亢婷 | 18207598386 | 药品市场推广主管/专员 | 28 | 1 | ping50@hotmail.com |
| 7 | 仰俊 | 13192184011 | 机场代表 | 24 | 0 | wcai@liang.net |
| 8 | 匡洁 | 13622482447 | 汽车电工 | 24 | 1 | htang@gmail.com |
| 9 | 程建华 | 13748396030 | 市场通路经理/主管 | 28 | 1 | fangguo@yahoo.com |
| 10 | 岳荣 | 15080695604 | 培训督导 | 24 | 1 | fanglong@ding.com |
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
10 rows in set (0.00 sec)
-- 查询数据
select * from tb_user where profession = '法务经理' and age = 27 and status = 1;
+----+--------+-------------+--------------+------+--------+----------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+--------------+------+--------+----------------+
| 1 | 费阳 | 13777763170 | 法务经理 | 27 | 1 | wyao@gmail.com |
+----+--------+-------------+--------------+------+--------+----------------+
1 row in set (0.01 sec)
explain select * from tb_user where profession = '法务经理' and age = 27 and status = 1;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 213 | const,const,const | 1 | 100.00 | NULL |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
-- 使用了索引字段 Using index
explain select id, profession from tb_user where profession = '法务经理' and age = 27 and status = 1;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 213 | const,const,const | 1 | 100.00 | Using index |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
-- 使用了索引字段 Using index
explain select id, profession, age, status from tb_user where profession = '法务经理' and age = 27 and status = 1;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 213 | const,const,const | 1 | 100.00 | Using index |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
explain select id, profession, age, status, name from tb_user where profession = '法务经理' and age = 27 and status = 1;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 213 | const,const,const | 1 | 100.00 | NULL |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------------------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
```
### 6.5、思考
问题：
一张表，有四个字段:
```
id, username, password, status
```
由于数据量较大，需要对以下SQL语句进行优化，该如何进行才是最优方案
```sql
select id, username, password from tb_user where username = 'Tom';
```
解答：
需要对`username, password`创建联合索引
联合索引的叶子节点存储了`id`字段，可以`避免回表查询`，从而提高查询效率
```sql
create index idx_user_username_password on tb_user (username, password);
```
### 6.6、前缀索引
当字段类型为字符串（varchar, text等）时，有时候需要索引很长的字符串，
这会让索引变得很大，查询时，浪费大量的磁盘IO，影响查询效率。
此时可以只将字符串的一部分前缀，建立索引，这样可以打打节约空间，从而提高索引效率。
1、语法
```sql
create index index_name on table_name (column(n));
```
2、前缀长度
可以根据索引的选择性来决定，而选择性是指不重复的索引值（基数）和数据表的记录总数的比值
索引选择性越高则查询效率越高
唯一索引的选择性是1，这是最好的索引选择性，性能也是最好的
```sql
-- 求取数据总条数
select count(*) from tb_user;
+----------+
| count(*) |
+----------+
| 10000 |
+----------+
1 row in set (0.07 sec)
-- 求取email不为空的数据条数
select count(email) from tb_user;
+--------------+
| count(email) |
+--------------+
| 10000 |
+--------------+
1 row in set (0.03 sec)
-- 求取email不重复的数据条数
select count(distinct email) from tb_user;
+-----------------------+
| count(distinct email) |
+-----------------------+
| 9569 |
+-----------------------+
1 row in set (0.02 sec)
-- 计算选择性
select count(distinct email) / count(*) from tb_user;
+----------------------------------+
| count(distinct email) / count(*) |
+----------------------------------+
| 0.9569 |
+----------------------------------+
1 row in set (0.01 sec)
-- 截取前缀计算选择性
select count(distinct substring(email, 1, 9)) / count(*) from tb_user;
+---------------------------------------------------+
| count(distinct substring(email, 1, 9)) / count(*) |
+---------------------------------------------------+
| 0.8633 |
+---------------------------------------------------+
1 row in set (0.02 sec)
```
建立前缀索引
```sql
-- 查看当前表中存在的索引
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 | 9804 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 9130 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 6232 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 7596 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
6 rows in set (0.05 sec)
-- 创建前缀索引
create index idx_email_5 on tb_user(email(5));
-- 再次查看索引（注意字段：Sub_part）
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 | 9804 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 9130 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 6232 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 7596 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_email_5 | 1 | email | A | 3955 | 5 | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
7 rows in set (0.01 sec)
```
使用索引
```sql ```sql
select * from tb_user where profession = '美术' and age > 22 and status = 1; -- 查询数据
+----+--------+-------------+------------+------+--------+------------+ select * from tb_user where email = 'wyao@gmail.com';
| id | name | phone | profession | age | status | email | +----+--------+-------------+--------------+------+--------+----------------+
+----+--------+-------------+------------+------+--------+------------+ | id | name | phone | profession | age | status | email |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com | +----+--------+-------------+--------------+------+--------+----------------+
+----+--------+-------------+------------+------+--------+------------+ | 1 | 费阳 | 13777763170 | 法务经理 | 27 | 1 | wyao@gmail.com |
1 row in set (0.00 sec) +----+--------+-------------+--------------+------+--------+----------------+
1 row in set (0.01 sec)
-- age使用了大于号>，只有profession和age用到了索引 -- 查看执行计划
explain select * from tb_user where profession = '美术' and age > 22 and status = 1; explain select * from tb_user where email = 'wyao@gmail.com';
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +----+-------------+---------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +----+-------------+---------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+
| 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 48 | NULL | 1 | 25.00 | Using index condition | | 1 | SIMPLE | tb_user | NULL | ref | idx_email_5 | idx_email_5 | 23 | const | 1 | 100.00 | Using where |
+----+-------------+---------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+
1 row in set, 1 warning (0.01 sec) 1 row in set, 1 warning (0.01 sec)
1 row in set, 1 warning (0.01 sec)
-- 三个字段都用到了索引
explain select * from tb_user where profession = '美术' and age >= 22 and status = 1;
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 53 | NULL | 1 | 25.00 | Using index condition |
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
``` ```
查询流程
![](img/pre-index.png)
## 7、索引失效的场景 ## 7、索引失效的场景
### 7.1、索引列运算 ### 7.1、索引列运算
...@@ -1455,199 +1904,34 @@ explain select * from tb_user where profession is null; ...@@ -1455,199 +1904,34 @@ explain select * from tb_user where profession is null;
``` ```
### 7.6、范围查询
### 7.6、SQL提示 联合索引中，出现范围查询（>、<），范围查询右侧的列索引失效
SQL提示是优化数据库的一个重要手段
简单来说，就是在SQL语句中加入一些认为的提示来达到优化操作的目的
```sql
-- 1、use index 推荐使用索引
explain select * from tb_user use index (idx_user_profession) where profession = '法务经理';
-- 2、ignore index 忽略使用索引
explain select * from tb_user ignore index (idx_user_profession) where profession = '法务经理';
-- 3、force index 强制使用索引
explain select * from tb_user force index (idx_user_profession) where profession = '法务经理';
```
测试数据准备
```sql
drop table if exists tb_user;
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(50) comment '专业',
age int comment '年龄',
status int comment '状态',
email varchar(50) comment '邮箱'
);
```
利用Python脚本生成10万条测试数据
```python
# 安装依赖 pip install faker records mysqlclient
from faker import Faker
import records
# 简体中文：zh_CN
faker = Faker(locale="zh_CN")
# 指定随机种子，确保每次生成的数据都是一致的
faker.seed(1)
# 生成数据插入 insert sql
def get_insert_sql(table_name, fields):
keys = ', '.join([f'`{key}`'.format(key) for key in fields])
values = ', '.join([f':{key}'.format(key) for key in fields])
return f'INSERT INTO `{table_name}` ({keys}) VALUES ({values})'
# 获取数据
def get_row():
return {
'name': faker.name(),
'phone': faker.phone_number(),
'email': faker.email(),
'age': faker.random_int(20, 30),
'status': faker.random_int(0, 1),
'profession': faker.job(),
}
def main():
db = records.Database('mysql://root:123456@localhost/data?charset=utf8')
# 10 * 1000 = 1万条数据
for i in range(10):
data = [get_row() for _ in range(1000)]
sql = get_insert_sql('tb_user', data[0].keys())
db.bulk_query(sql, data)
if __name__ == '__main__':
main()
```
查看生成的测试数据
```sql
mysql> select count(*) from tb_user;
+----------+
| count(*) |
+----------+
| 10000 |
+----------+
select * from tb_user limit 10;
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
| id | name | phone | profession | age | status | email |
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
| 1 | 费阳 | 13777763170 | 法务经理 | 27 | 1 | wyao@gmail.com |
| 2 | 祁海燕 | 13400806360 | 日式厨师 | 23 | 0 | jwan@jin.cn |
| 3 | 姬秀英 | 18281241586 | 食品/饮料研发 | 29 | 0 | li97@wang.cn |
| 4 | 官桂芳 | 15625851781 | 前台接待/总机/接待生 | 20 | 1 | fpeng@chang.cn |
| 5 | 应秀珍 | 13030388368 | 酒店前台 | 20 | 1 | qiang48@hotmail.com |
| 6 | 亢婷 | 18207598386 | 药品市场推广主管/专员 | 28 | 1 | ping50@hotmail.com |
| 7 | 仰俊 | 13192184011 | 机场代表 | 24 | 0 | wcai@liang.net |
| 8 | 匡洁 | 13622482447 | 汽车电工 | 24 | 1 | htang@gmail.com |
| 9 | 程建华 | 13748396030 | 市场通路经理/主管 | 28 | 1 | fangguo@yahoo.com |
| 10 | 岳荣 | 15080695604 | 培训督导 | 24 | 1 | fanglong@ding.com |
+----+-----------+-------------+---------------------------------+------+--------+---------------------+
10 rows in set (0.00 sec)
```
创建索引
```sql
-- 创建普通索引
create index idx_user_name on tb_user (name);
-- 创建唯一索引
create unique index idx_user_phone on tb_user (phone);
-- 创建联合索引
create index idx_user_profession_age_status on tb_user (profession, age, status);
-- 创建普通索引
create index idx_user_email on tb_user (email);
-- 创建索引
create index idx_user_age on tb_user ( age );
-- 查看索引
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 | 9804 | NULL | NULL | | BTREE | | | YES | NULL |
| tb_user | 0 | idx_user_phone | 1 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_name | 1 | name | A | 9130 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 1 | profession | A | 948 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 2 | age | A | 6232 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_profession_age_status | 3 | status | A | 7596 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_email | 1 | email | A | 9569 | NULL | NULL | YES | BTREE | | | YES | NULL |
| tb_user | 1 | idx_user_age | 1 | age | A | 11 | NULL | NULL | YES | BTREE | | | YES | NULL |
+---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+
8 rows in set (0.03 sec)
```
查看执行计划
```sql ```sql
mysql> explain select * from tb_user where profession = '法务经理'; select * from tb_user where profession = '美术' and age > 22 and status = 1;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +----+--------+-------------+------------+------+--------+------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | | id | name | phone | profession | age | status | email |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +----+--------+-------------+------------+------+--------+------------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 203 | const | 12 | 100.00 | NULL | | 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +----+--------+-------------+------------+------+--------+------------+
1 row in set, 1 warning (0.00 sec) 1 row in set (0.00 sec)
-- 创建一个单列索引
create index idx_user_profession on tb_user (profession);
-- 性能分析
explain select * from tb_user where profession = '法务经理';
+----+-------------+---------+------------+------+----------------------------------------------------+--------------------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+----------------------------------------------------+--------------------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status,idx_user_profession | idx_user_profession_age_status | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+----------------------------------------------------+--------------------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)
-- 查看执行计划（use index）使用单列索引idx_user_profession
explain select * from tb_user use index (idx_user_profession) where profession = '法务经理';
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession | idx_user_profession | 203 | const | 12 | 100.00 | NULL |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.01 sec)
-- 查看执行计划（ignore index）,忽略单列索引idx_user_profession -- age使用了大于号>，只有profession和age用到了索引
explain select * from tb_user ignore index (idx_user_profession) where profession = '法务经理'; explain select * from tb_user where profession = '美术' and age > 22 and status = 1;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession_age_status | idx_user_profession_age_status | 203 | const | 12 | 100.00 | NULL | | 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 48 | NULL | 1 | 25.00 | Using index condition |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.01 sec) 1 row in set, 1 warning (0.01 sec)
-- 查看执行计划（force index）强制使用单列索引idx_user_profession -- 三个字段都用到了索引
explain select * from tb_user force index (idx_user_profession) where profession = '法务经理'; explain select * from tb_user where profession = '美术' and age >= 22 and status = 1;
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+ +----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+ +----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| 1 | SIMPLE | tb_user | NULL | ref | idx_user_profession | idx_user_profession | 203 | const | 12 | 100.00 | NULL | | 1 | SIMPLE | tb_user | NULL | range | idx_user_profession_age_status | idx_user_profession_age_status | 53 | NULL | 1 | 25.00 | Using index condition |
+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+ +----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec) 1 row in set, 1 warning (0.00 sec)
``` ```
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