diff --git a/blog/mysq-advance/index.md b/blog/mysq-advance/index.md index efe7a9fb78f10534c2c33e163afc91998639bf1e..1f62fcd14b8cdaf26afc20c60f875c5d7a5b3d79 100644 --- a/blog/mysq-advance/index.md +++ b/blog/mysq-advance/index.md @@ -36,4 +36,5 @@ 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=92&spm_id_from=pageDriver \ No newline at end of file + +https://www.bilibili.com/video/BV1Kr4y1i7ru?p=97&spm_id_from=pageDriver \ No newline at end of file diff --git a/blog/mysq-advance/sql-optimization.md b/blog/mysq-advance/sql-optimization.md index 0bbd47c0492316195bd67993008edade50686307..59556adf65197fe4a72bff6a63100bd3d5b715a3 100644 --- a/blog/mysq-advance/sql-optimization.md +++ b/blog/mysq-advance/sql-optimization.md @@ -454,3 +454,501 @@ mysql> show variables like 'sort_buffer_size'; +------------------+--------+ 1 row in set (0.03 sec) ``` + +## 4、group by优化 + +1. 分组操作时，可以通过索引来提高效率 + +2. 分组操作时，索引的使用也是满足`最左前缀法则`的 + +示例 + +```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 | 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 | +| tb_user | 1 | idx_user_age_phone | 1 | age | A | 11 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_age_phone | 2 | phone | A | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_age_phone_ad | 1 | age | A | 11 | NULL | NULL | YES | BTREE | | | YES | NULL | +| tb_user | 1 | idx_user_age_phone_ad | 2 | phone | D | 9804 | NULL | NULL | YES | BTREE | | | YES | NULL | ++---------+------------+--------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +9 rows in set (0.06 sec) + +-- 删除索引 +drop index idx_user_profession_age_status on tb_user; + +drop index idx_email_5 on tb_user; + +drop index idx_user_age_phone on tb_user; + +drop index idx_user_age_phone_ad on tb_user; + +-- 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 | ++---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ +1 row in set (0.01 sec) + +-- 执行分组操作，根据profession字段分组 +select profession, count(*) from tb_user group by profession; ++---------------------------------------------------+----------+ +| profession | count(*) | ++---------------------------------------------------+----------+ +| 法务经理 | 12 | +| 日式厨师 | 7 | +| 食品/饮料研发 | 7 | +| 前台接待/总机/接待生 | 10 | +| 酒店前台 | 8 | +| 药品市场推广主管/专员 | 5 | +| 机场代表 | 10 | ++---------------------------------------------------+----------+ +948 rows in set (0.02 sec) + +-- 查看执行计划 Using temporary +explain select profession, count(*) from tb_user group by profession; ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-----------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-----------------+ +| 1 | SIMPLE | tb_user | NULL | ALL | NULL | NULL | NULL | NULL | 9804 | 100.00 | Using temporary | ++----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-----------------+ +1 row in set, 1 warning (0.01 sec) + +-- 创建索引 +create index idx_user_profession_age_status on tb_user(profession, age, status); + +-- 执行分组操作，根据profession字段分组 Using index +explain select profession, count(*) from tb_user group by profession; ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | index | idx_user_profession_age_status | idx_user_profession_age_status | 213 | NULL | 9804 | 100.00 | Using index | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-------------+ +1 row in set, 1 warning (0.01 sec) + +-- 执行分组操作，根据age字段分组 Using index; Using temporary(临时表，性能较低) +explain select age, count(*) from tb_user group by age; ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+------------------------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+------------------------------+ +| 1 | SIMPLE | tb_user | NULL | index | idx_user_profession_age_status | idx_user_profession_age_status | 213 | NULL | 9804 | 100.00 | Using index; Using temporary | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+------------------------------+ +1 row in set, 1 warning (0.00 sec) + +-- 执行分组操作，根据profession, age字段分组,满足最左前缀法则 +explain select profession, age, count(*) from tb_user group by profession, age; ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-------------+ +| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-------------+ +| 1 | SIMPLE | tb_user | NULL | index | idx_user_profession_age_status | idx_user_profession_age_status | 213 | NULL | 9804 | 100.00 | Using index | ++----+-------------+---------+------------+-------+--------------------------------+--------------------------------+---------+------+------+----------+-------------+ +1 row in set, 1 warning (0.01 sec) + +-- 增加过滤条件，再根据age字段分组 Using index，满足最左前缀法则 +explain select age, count(*) from tb_user where profession = '项目经理' group by age; ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------------+ +| 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 | Using index | ++----+-------------+---------+------------+------+--------------------------------+--------------------------------+---------+-------+------+----------+-------------+ +1 row in set, 1 warning (0.00 sec) + +``` + +## 5、limit 优化 + +当MySQL需要取前2000000条记录时，仅仅返回`2000000- 2000010`的记录，其他记录丢弃，查询排序的代价非常大 + +优化思路： + +一般分页查询时，通过创建`覆盖索引`能够比较好的提高性能，可以通过覆盖索引加子查询形式进行优化 + + +示例 + +```sql +-- 查看数据总数 1000W条数据 +mysql> select count(*) from tb_sku; ++----------+ +| count(*) | ++----------+ +| 10000000 | ++----------+ +1 row in set (3.94 sec) + +-- 取第一页数据 +mysql> select * from tb_sku limit 0, 10; ++---------+--------------------------------------+ +| id | uuid | ++---------+--------------------------------------+ +| 6162096 | 0000012f-4a44-4b8b-93e4-4dcd99ecff22 | +| 112574 | 00000274-d865-40f9-b799-4c0fbdd8a21d | +| 9618175 | 000004a3-3f93-4a7b-8a98-f17468445e3a | +| 3774310 | 000004ea-9025-4ba4-89eb-d30e7e14185e | +| 9781779 | 000007e3-7e71-4e90-b681-fca25137fe08 | +| 4457266 | 0000081b-aa05-4194-af4e-6ad0a750b0ab | +| 3950776 | 00000a39-428c-4cca-aaf7-f9e63889272f | +| 7617466 | 00000c69-b2c5-4f4a-b829-54b208bdce90 | +| 969786 | 00000df2-c3ff-478b-bd6c-a5ebcf94ad11 | +| 9704958 | 00000ec4-2716-4ee4-9165-ba84ecd05050 | ++---------+--------------------------------------+ +10 rows in set (0.00 sec) + +-- 取第二页数据 +mysql> select * from tb_sku limit 10, 10; ++---------+--------------------------------------+ +| id | uuid | ++---------+--------------------------------------+ +| 9563294 | 000010f8-f717-44d9-9f7e-acefd48d26b8 | +| 5652396 | 0000112c-0f25-47d3-839b-3b929d0d7adb | +| 1290981 | 0000121a-01ba-47aa-bfa3-e97693a92ad7 | +| 8107372 | 000012c1-6a61-42e6-8769-0bb3dcd61097 | +| 7842196 | 00001375-b43d-407a-9163-ce633ed64592 | +| 2206208 | 00001448-58e8-478b-92a2-c74de197b659 | +| 9808308 | 00001542-00b6-4207-8c67-34ed296996d6 | +| 3282004 | 00001853-abb3-4fb6-ae18-122dc5658fd2 | +| 957944 | 00001a00-c8cd-4492-b919-127345271172 | +| 7964789 | 00001cfe-679d-43f0-bbaa-d21676f45b70 | ++---------+--------------------------------------+ +10 rows in set (0.00 sec) + +-- 增加分页 +mysql> select * from tb_sku limit 9000000, 10; ++---------+--------------------------------------+ +| id | uuid | ++---------+--------------------------------------+ +| 7919352 | e65fe47c-c7a7-4440-929d-87d64234b785 | +| 5709825 | e65fe68a-b28e-4a8d-bab8-64c03ed00f37 | +| 4319305 | e65fe6df-1299-4960-9450-515369725171 | +| 1116567 | e65fe75a-3579-49e1-838d-3ce3c5c754f9 | +| 3200374 | e65fe89f-2d5b-4928-8c96-89aeee890418 | +| 8207624 | e65fe9ae-17f4-4383-84a8-6c4913ad81f9 | +| 152637 | e65fee7f-25ce-4169-8d39-6dd4e6a3db57 | +| 8533603 | e65ff27a-fcbf-4d51-b85a-db6322e7b425 | +| 3249838 | e65ff2e4-b442-4f7c-b11c-422832afdef5 | +| 2665508 | e65ff482-664b-49e9-ab8c-017499fd70df | ++---------+--------------------------------------+ +10 rows in set (1.87 sec) + +mysql> select id from tb_sku order by id limit 9000000, 10; ++---------+ +| id | ++---------+ +| 9000001 | +| 9000002 | +| 9000003 | +| 9000004 | +| 9000005 | +| 9000006 | +| 9000007 | +| 9000008 | +| 9000009 | +| 9000010 | ++---------+ +10 rows in set (1.65 sec) + +-- 不支持分页子查询 +mysql> select * from tb_sku where id in (select id from tb_sku order by id limit 9000000, 10); +ERROR 1235 (42000): This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' + +-- 正确的查询方式 +mysql> select s.* from tb_sku s, (select id from tb_sku order by id limit 9000000, 10) a where s.id = a.id; ++---------+--------------------------------------+ +| id | uuid | ++---------+--------------------------------------+ +| 9000001 | f7b44618-8bd2-4a5f-9cf9-ba6734966905 | +| 9000002 | 86863769-ead4-4e8a-ab81-4c32429dddcf | +| 9000003 | 4471b035-cb9b-4958-ab61-4159ff24df48 | +| 9000004 | a11746eb-482f-4d8d-90fb-32a7e156c34a | +| 9000005 | c5ded2ef-8995-43fb-9332-62c1dd1922bc | +| 9000006 | 4d02f0f5-5e71-4f5c-8006-369ef1dcd6d6 | +| 9000007 | efe87680-b59b-4999-89b7-de4d07704527 | +| 9000008 | 27b2f930-fbb5-476f-a470-1a42bb4e4d2e | +| 9000009 | 7c54b9b0-e41e-439e-b907-8c25ba364e7f | +| 9000010 | 3d576629-d70f-470c-bef3-d3a3c815f0cc | ++---------+--------------------------------------+ +10 rows in set (1.59 sec) +``` + +## 6、count 优化 + +```sql +select count(*) from tb_user; +``` + +- MyISAM引擎，把一个表的总行数存在了磁盘上，因此执行`count(*)`的时候会直接返回这个数，效率很高 +- InnoDB引擎，执行`count(*)` 的时候，需要把数据一行一行地从引擎里读取出来，让后累计计数 + +### 6.1、优化思路 + +自己计数 + +例如：借助redis，添加数据`+1`, 删除数据`-1` + +### 6.2、count的几种用法 + +`count()` 是一个聚合函数，对于返回的结果集，一行行的判断，如果count函数的参数不是null, 累计值就+1，否则不加，最后返回累计值 + +用法： + +1. `count(*)` + - InnoDB引擎并不会把全部字段取出来，而是专门做了优化，不取值，服务层直接按行进行累加 + +2. `count(主键)` + - InnoDB引擎会遍历整张表，把每一行的主键id值取出来，返回给服务层。服务层拿到主键后，直接按行进行累加 + - 主键不可能为null + +3. `count(字段)` + - 没有`not null`约束: InnoDB引擎会遍历整张表，把每一行的字段值都取出来，返回给服务层，服务层判断是否为null，不为null,计数累加 + - 有`not null`约束: InnoDB引擎会遍历整张表，把每一行的字段值都取出来，返回给服务层，直接按行进行累加 + +4. `count(1)` + - InnoDB引擎会遍历整张表，但是不取值。服务层对于返回的每一行，放一个数字`1`进去，直接按行进行累加 + +效率排序： + +```sql +count(字段) < count(主键id) < count(1) ≈ count(*) +``` + +所以尽量使用: `count(*)` + +示例 + +```sql +mysql> select * from tb_user limit 3; ++----+-----------+-------------+---------------------+------+--------+----------------+ +| 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 | ++----+-----------+-------------+---------------------+------+--------+----------------+ +3 rows in set (0.01 sec) + +-- 修改其中一个值为null +update tb_user set profession = null where id = 1; + +mysql> select * from tb_user limit 3; ++----+-----------+-------------+---------------------+------+--------+----------------+ +| id | name | phone | profession | age | status | email | ++----+-----------+-------------+---------------------+------+--------+----------------+ +| 1 | 费阳 | 13777763170 | NULL | 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 | ++----+-----------+-------------+---------------------+------+--------+----------------+ +3 rows in set (0.01 sec) + +mysql> select count(*) from tb_user; ++----------+ +| count(*) | ++----------+ +| 10000 | ++----------+ +1 row in set (0.01 sec) + +mysql> select count(id) from tb_user; ++-----------+ +| count(id) | ++-----------+ +| 10000 | ++-----------+ +1 row in set (0.00 sec) + +mysql> select count(profession) from tb_user; ++-------------------+ +| count(profession) | ++-------------------+ +| 9999 | ++-------------------+ +1 row in set (0.00 sec) + +mysql> select count(null) from tb_user; ++-------------+ +| count(null) | ++-------------+ +| 0 | ++-------------+ +1 row in set (0.00 sec) + +-- 传递一个数，可以是任何数 +mysql> select count(1) from tb_user; ++----------+ +| count(1) | ++----------+ +| 10000 | ++----------+ +1 row in set (0.01 sec) + + +``` + + +## 7、update 优化 + +InnoDB的行锁是针对索引加的锁，不是针对记录加的锁，并且该索引不能失效，否则会从行锁升级为表锁。 + + +1、主键作为查询条件更新数据 + +```sql +select * from tb_course; ++----+--------+ +| id | name | ++----+--------+ +| 1 | 语文 | +| 2 | 数学 | +| 3 | 英语 | +| 4 | 历史 | +| 5 | 化学 | ++----+--------+ +5 rows in set (0.02 sec) + + +-- 开启事务1 +begin; +update tb_course set name = '语文A' where id = 1; +-- 此时id=1这一行被锁住，添加行锁 + +-- 新窗口开启事务2 +begin; +update tb_course set name = '历史A' where id = 4; + +-- 事务1提交 +commit; + +-- 事务2提交 +commit; + +select * from tb_course; ++----+---------+ +| id | name | ++----+---------+ +| 1 | 语文A | +| 2 | 数学 | +| 3 | 英语 | +| 4 | 历史A | +| 5 | 化学 | ++----+---------+ +5 rows in set (0.00 sec) +``` + +2、普通字段作为查询条件更新数据 + +```sql +-- 开启事务1 +begin; +update tb_course set name = '语文B' where name = '语文A'; +-- 由于name字段没有索引，添加表锁 + +-- 新窗口开启事务2 +begin; +update tb_course set name = '历史B' where name = '历史A'; +-- 此时SQL语句会卡主，不再执行 + +-- 事务1提交 +commit; +-- 此时事务2SQL语句会继续执行 + +-- 事务2提交 +commit; + +select * from tb_course; ++----+---------+ +| id | name | ++----+---------+ +| 1 | 语文B | +| 2 | 数学 | +| 3 | 英语 | +| 4 | 历史B | +| 5 | 化学 | ++----+---------+ +5 rows in set (0.00 sec) +``` + +3、索引字段作为查询条件更新数据 +```sql +-- 创建索引 +create index idx_course_name on tb_course(name); + +-- 开启事务1 +begin; +update tb_course set name = '语文C' where name = '语文B'; +-- 由于name字段有索引，添加行锁 + +-- 新窗口开启事务2 +begin; +update tb_course set name = '历史C' where name = '历史B'; +-- 此时SQL语句没有卡主，执行完成 + +-- 事务1提交 +commit; + +-- 事务2提交 +commit; + +select * from tb_course; ++----+---------+ +| id | name | ++----+---------+ +| 5 | 化学 | +| 4 | 历史C | +| 2 | 数学 | +| 3 | 英语 | +| 1 | 语文C | ++----+---------+ +5 rows in set (0.01 sec) +``` + +## 8、总结 + +1、插入数据 + +- insert 批量插入、手动控制事务、主键顺序插入 +- 大批量数据插入：`load data local infile` + +2、主键优化 + +- InnoDB引擎数据组织方式：基于索引 +- 页分裂：插入数据(主键乱序插入) +- 页合并：删除数据 +- 主键长度尽可能短，顺序插入 +- 推荐auto_increment, 避免uuid + +3、order by 优化 + +- using index：直接通过索引返回数据，性能高 +- using filesort：需要将返回的结果在排序缓冲区排序,甚至可能用到磁盘文件 + +- 尽量使用覆盖索引 +- 尽量对排序字段建立索引 + +- 同为升序或同为降序可以用到索引 +- 创建索引时注意其排序方式asc/desc + +4、group by 优化 + +- 索引、多字段分组满足最左前缀法则 + +5、limit 优化 + +- 覆盖索引 + 子查询 + +6、count 优化 + +- 推荐使用`count(*)` +- 自己计数 + +7、update 优化 + +- 根据索引（id）字段更新，避免行锁升级为表锁，降低数据库并发访问性 + diff --git a/blog/php-mysql/index.md b/blog/php-mysql/index.md index 94ab4c42a69c08718dcfe7285c333d8ac0913faa..b11cc08220d30f22be522c4e82389029a197c20f 100644 --- a/blog/php-mysql/index.md +++ b/blog/php-mysql/index.md @@ -16,7 +16,7 @@ 7. [数据类型-整数](blog/php-mysql/sql-int.md) -[数据类型-小数](blog/php-mysql/sql-float.md) +8. [数据类型-小数](blog/php-mysql/sql-float.md) [数据类型-时间日期类型](blog/php-mysql/sql-datetime.md)