diff --git a/blog/mysq-advance/index.md b/blog/mysq-advance/index.md index feda5a5179efc8d620e091df0021dda9f2ae5173..258cd53778ec03d9d451c58de0feea959743c946 100644 --- a/blog/mysq-advance/index.md +++ b/blog/mysq-advance/index.md @@ -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 diff --git a/blog/mysq-advance/mysql-index.md b/blog/mysq-advance/mysql-index.md index f80da2fda94c4ae2112434734084f66ff770e915..fb03854ddce5ab184817ce7110c58e4b8dae0af4 100644 --- a/blog/mysq-advance/mysql-index.md +++ b/blog/mysq-advance/mysql-index.md @@ -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) +``` + diff --git a/blog/php-mysql/sql-function.md b/blog/php-mysql/sql-function.md index e471d179cfc05edb68cb4de3dcd12bb23823ed27..7ece629c04929492749a731998c706c072b7059d 100644 --- a/blog/php-mysql/sql-function.md +++ b/blog/php-mysql/sql-function.md @@ -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 diff --git a/doc/index.md b/doc/index.md index 5281ded7cbd39528fd668e02adcf399ceafd32de..fdd6dadef39c56d473d23aa6185f03f010577ffb 100644 --- a/doc/index.md +++ b/doc/index.md @@ -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.