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“cb70c362dc42f7fa40ed83963bdb0a855ab53ab1”上不存在“...reference/apis/js-apis-file-volumemanager.md”
提交 aa33159d 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
- 3. [https://www.yuque.com/heychu/akbndd/zhuxqd](https://www.yuque.com/heychu/akbndd/zhuxqd)
https://www.bilibili.com/video/BV1Kr4y1i7ru?p=79&spm_id_from=pageDriver
\ No newline at end of file
https://www.bilibili.com/video/BV1Kr4y1i7ru?p=84&spm_id_from=pageDriver
\ No newline at end of file
blog/mysq-advance/mysql-index.md
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......@@ -6,7 +6,8 @@
4. 索引语法
5. SQL 性能分析
6. 索引使用
7. 索引设计原则
7. 索引失效的场景
8. 索引设计原则
## 1. 索引概述
......@@ -241,23 +242,23 @@ create table tb_user(
-- 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');
values ('张飞', '17712345678', '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');
values ('关羽', '17722345678', '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');
values ('刘备', '17732345678', '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');
values ('孙权', '17742345678', '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 |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
| 2 | 关羽 | 17722345678 | 物理 | 24 | 1 | 3339@qq.com |
| 3 | 刘备 | 17732345678 | 数学 | 25 | 0 | 666@qq.com |
| 4 | 孙权 | 17742345678 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+-------------+
4 rows in set (0.00 sec)
......@@ -820,10 +821,10 @@ 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 |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
| 2 | 关羽 | 17722345678 | 物理 | 24 | 1 | 3339@qq.com |
| 3 | 刘备 | 17732345678 | 数学 | 25 | 0 | 666@qq.com |
| 4 | 孙权 | 17742345678 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+-------------+
4 rows in set (0.00 sec)
......@@ -842,7 +843,7 @@ mysql> show index from tb_user;
7 rows in set (0.05 sec)
mysql> explain select * from tb_user where phone = '15210231227';
mysql> explain select * from tb_user where phone = '17712345678';
+----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+
......@@ -1028,10 +1029,10 @@ 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 |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
| 2 | 关羽 | 17722345678 | 物理 | 24 | 1 | 3339@qq.com |
| 3 | 刘备 | 17732345678 | 数学 | 25 | 0 | 666@qq.com |
| 4 | 孙权 | 17742345678 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+-------------+
4 rows in set (0.01 sec)
......@@ -1055,7 +1056,7 @@ select * from tb_user where profession = '美术' and age = 23 and status = 1;
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
......@@ -1132,7 +1133,7 @@ select * from tb_user where profession = '美术' and age > 22 and status = 1;
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
......@@ -1167,10 +1168,10 @@ 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 |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
| 2 | 关羽 | 17722345678 | 物理 | 24 | 1 | 3339@qq.com |
| 3 | 刘备 | 17732345678 | 数学 | 25 | 0 | 666@qq.com |
| 4 | 孙权 | 17742345678 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+-------------+
4 rows in set (0.00 sec)
......@@ -1190,16 +1191,16 @@ mysql> show index from tb_user;
7 rows in set (0.01 sec)
-- 按照手机号查询数据
mysql> select * from tb_user where phone = '15210231227';
mysql> select * from tb_user where phone = '17712345678';
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
-- 分析索引使用情况
explain select * from tb_user where phone = '15210231227';
explain select * from tb_user where phone = '17712345678';
+----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+----------------+----------------+---------+-------+------+----------+-------+
......@@ -1212,7 +1213,7 @@ select * from tb_user where substring(phone, 10, 2) = '27';
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
......@@ -1232,16 +1233,16 @@ explain select * from tb_user where substring(phone, 10, 2) = '27';
```sql
-- 字符串查询可以不加引号
select * from tb_user where phone = 15210231227;
select * from tb_user where phone = 17712345678;
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
-- 不加引号的字符串查询没有走索引
explain select * from tb_user where phone = 15210231227;
explain select * from tb_user where phone = 17712345678;
+----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+
......@@ -1261,7 +1262,7 @@ select * from tb_user where profession like '美%';
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 15210231227 | 美术 | 23 | 1 | 123@qq.com |
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
......@@ -1286,4 +1287,367 @@ explain select * from tb_user where profession like '%术';
1 row in set, 1 warning (0.01 sec)
```
### 7.4、or连接的条件
用or分割开的条件，如果or前的条件中有的列有索引，而后面的列中没有索引，那么涉及的索引都不会被用到
```sql
select * from tb_user where id = 1 or age = 23;
select * from tb_user where phone = '17742345678' or age = 23;
```
由于age没有索引，所以即使id，phone有索引，索引也会失效。age也需要建立索引
示例
```sql
-- 查看表数据
select * from tb_user;
+----+--------+-------------+------------+------+--------+-------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+-------------+
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
| 2 | 关羽 | 17722345678 | 物理 | 24 | 1 | 3339@qq.com |
| 3 | 刘备 | 17732345678 | 数学 | 25 | 0 | 666@qq.com |
| 4 | 孙权 | 17742345678 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+-------------+
4 rows in set (0.01 sec)
-- 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 | 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 (0.05 sec)
-- 查询数据
select * from tb_user where id = 1 or age = 23;
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 1 | 张飞 | 17712345678 | 美术 | 23 | 1 | 123@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
-- 分析
explain select * from tb_user where id = 1 or age = 23;
+----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+
| 1 | SIMPLE | tb_user | NULL | ALL | PRIMARY | NULL | NULL | NULL | 4 | 43.75 | Using where |
+----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
-- 分析
explain select * from tb_user where phone = '17742345678' or age = 23;
+----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+
| 1 | SIMPLE | tb_user | NULL | ALL | idx_user_phone | NULL | NULL | NULL | 4 | 43.75 | Using where |
+----+-------------+---------+------------+------+----------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.15 sec)
-- 创建索引
create index idx_user_age on tb_user ( age );
-- 再次分析性能
explain select * from tb_user where id = 1 or age = 23;
+----+-------------+---------+------------+-------------+----------------------+----------------------+---------+------+------+----------+------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------------+----------------------+----------------------+---------+------+------+----------+------------------------------------------------+
| 1 | SIMPLE | tb_user | NULL | index_merge | PRIMARY,idx_user_age | PRIMARY,idx_user_age | 4,5 | NULL | 2 | 100.00 | Using union(PRIMARY,idx_user_age); Using where |
+----+-------------+---------+------------+-------------+----------------------+----------------------+---------+------+------+----------+------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
explain select * from tb_user where phone = '17742345678' or age = 23;
+----+-------------+---------+------------+-------------+-----------------------------+-----------------------------+---------+------+------+----------+-------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------------+-----------------------------+-----------------------------+---------+------+------+----------+-------------------------------------------------------+
| 1 | SIMPLE | tb_user | NULL | index_merge | idx_user_phone,idx_user_age | idx_user_phone,idx_user_age | 47,5 | NULL | 2 | 100.00 | Using union(idx_user_phone,idx_user_age); Using where |
+----+-------------+---------+------------+-------------+-----------------------------+-----------------------------+---------+------+------+----------+-------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
```
### 7.5、数据分布影响
如果MySQL性能评估使用索引比全表更慢，则不使用索引。
```sql
select * from tb_user where phone >= '17742345678';
+----+--------+-------------+------------+------+--------+------------+
| id | name | phone | profession | age | status | email |
+----+--------+-------------+------------+------+--------+------------+
| 4 | 孙权 | 17742345678 | 语文 | 20 | 1 | 111@qq.com |
+----+--------+-------------+------------+------+--------+------------+
1 row in set (0.00 sec)
explain select * from tb_user where phone >= '17742345678';
+----+-------------+---------+------------+-------+----------------+----------------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+----------------+----------------+---------+------+------+----------+-----------------------+
| 1 | SIMPLE | tb_user | NULL | range | idx_user_phone | idx_user_phone | 47 | NULL | 1 | 100.00 | Using index condition |
+----+-------------+---------+------------+-------+----------------+----------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)
explain select * from tb_user where phone >= '17712345670';
+----+-------------+---------+------------+-------+----------------+----------------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+----------------+----------------+---------+------+------+----------+-----------------------+
| 1 | SIMPLE | tb_user | NULL | range | idx_user_phone | idx_user_phone | 47 | NULL | 4 | 100.00 | Using index condition |
+----+-------------+---------+------------+-------+----------------+----------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)
```
`is null` 和 `is not null` 走不走索引，主要看表中的数据。
```sql
-- is null
explain select * from tb_user where profession is null;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+
| 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 | 43 | const | 1 | 100.00 | Using index condition |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+
1 row in set, 1 warning (0.01 sec)
-- is not null
explain select * from tb_user where profession is not null;
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| 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 | 43 | NULL | 4 | 100.00 | Using index condition |
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)
-- 将数据更新为null
update tb_user set profession = null;
-- 再次查看性能
explain select * from tb_user where profession is null;
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+
| 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 | 43 | const | 4 | 100.00 | Using index condition |
+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)
-- is not null
explain select * from tb_user where profession is not null;
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
| 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 | 43 | NULL | 1 | 100.00 | Using index condition |
+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)
```
### 7.6、SQL提示
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)
```
blog/php-mysql/sql-function.md
浏览文件 @ aa33159d
......@@ -23,7 +23,7 @@ ltrim | 消除左边的空格
left(str, length) | 左侧开始截取字符串，直到指定位置
right(str, length) | 右侧开始截取字符串，直到指定位置
mid | 从中间指定位置开始截取，如果不指定截取长度，直接到最后
`substring(str, index, [length]`) | 从指定位置开始，指定截取长度
`substring(str, index, [length])` | 从指定位置开始，指定截取长度
substring_index(str, delim, count) | 按照关键字截取
示例
......
doc/index.md
浏览文件 @ aa33159d
......@@ -32,7 +32,7 @@
Logo：https://www.logoly.pro/
[docsify](https://docsify.js.org/)：快速帮你生成文档网站
[docsify](https://docsify.js.org/#/zh-cn/)：快速帮你生成文档网站
[Prism](https://prismjs.com/) Prism is a lightweight, extensible syntax highlighter, built with modern web standards in mind.
......
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