diff --git a/blog/mysq-advance/img/cover-index.png b/blog/mysq-advance/img/cover-index.png new file mode 100644 index 0000000000000000000000000000000000000000..f10dc3b3196ff815e0a229036d6e48122ca24c9d Binary files /dev/null and b/blog/mysq-advance/img/cover-index.png differ diff --git a/blog/mysq-advance/img/pre-index.png b/blog/mysq-advance/img/pre-index.png new file mode 100644 index 0000000000000000000000000000000000000000..d72758e08533bb1d4a35a4295d92b593d86b5ea2 Binary files /dev/null and b/blog/mysq-advance/img/pre-index.png differ diff --git a/blog/mysq-advance/index.md b/blog/mysq-advance/index.md index 258cd53778ec03d9d451c58de0feea959743c946..70880a13772c7cbad1323d38aa5236e43f44cf68 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=84&spm_id_from=pageDriver \ No newline at end of file +https://www.bilibili.com/video/BV1Kr4y1i7ru?p=86&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 fb03854ddce5ab184817ce7110c58e4b8dae0af4..5b214c23dedfba539cdc7970d334b9cce66ff1ff 100644 --- a/blog/mysq-advance/mysql-index.md +++ b/blog/mysq-advance/mysql-index.md @@ -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) ``` -### 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 -select * from tb_user where profession = '美术' and age > 22 and status = 1; -+----+--------+-------------+------------+------+--------+------------+ -| 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) +-- 查询数据 +select * from tb_user where email = 'wyao@gmail.com'; ++----+--------+-------------+--------------+------+--------+----------------+ +| 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) --- age使用了大于号>，只有profession和age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 | 48 | NULL | 1 | 25.00 | Using index condition | -+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ +-- 查看执行计划 +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 | ++----+-------------+---------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+ +| 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) - --- 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 | -+----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ -1 row in set, 1 warning (0.00 sec) ``` +查询流程 + +![](img/pre-index.png) + ## 7、索引失效的场景 ### 7.1、索引列运算 @@ -1455,199 +1904,34 @@ explain select * from tb_user where profession is null; ``` +### 7.6、范围查询 -### 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 +联合索引中，出现范围查询（>、<），范围查询右侧的列索引失效 ```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) +select * from tb_user where profession = '美术' and age > 22 and status = 1; ++----+--------+-------------+------------+------+--------+------------+ +| 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) --- 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 | -+----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------+ +-- age使用了大于号>，只有profession和age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 | 48 | NULL | 1 | 25.00 | Using index condition | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ 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 | -+----+-------------+---------+------------+------+---------------------+---------------------+---------+-------+------+----------+-------+ +-- 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 | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-----------------------+ 1 row in set, 1 warning (0.00 sec) ``` - -