下文内容主要给大家带来MySQL8的数据库优化讲义，这里所讲到的知识，与书籍略有不同，都是创新互联专业技术人员在与用户接触过程中，总结出来的，具有一定的经验分享价值，希望给广大读者带来帮助。

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EXPLAIN

EXPLAIN
select dept_name from dept_emp join employees on dept_emp.emp_no=employees.emp_no join departments on departments.dept_no=dept_emp.dept_no where employees.first_name='Aamer';

EXPLAIN format=JSON select dept_name from dept_emp join employees on dept_emp.emp_no=employees.emp_no join departments on departments.dept_no=dept_emp.dept_no where employees.first_name='Aamer';

mysql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
|              30 |
+-----------------+
1 row in set (0.01 sec)

mysql> explain format=json for connection 30\G
ERROR 3012 (HY000): EXPLAIN FOR CONNECTION command is supported only for SELECT/UPDATE/INSERT/DELETE/REPLACE

mysql> pager grep rows

mysql> SELECT e.emp_no,salary from  salaries s join employees e on s.emp_no=e.emp_no where first_name='Adam';
2384 rows in set (0.24 sec)

mysql> pager
Default pager wasn't set, using stdout.

mysqlslap

mysqlslap 对于模拟多个用户同时对 MySQL 发起“进攻”提供了方便。同时详细的提供了“高负荷*** MySQL”的详细数据报告。

#mysqlslap -uroot -p --create-schema=employees --query="SELECT e.emp_no,salary from  salaries s join employees e on s.emp_no=e.emp_no where first_name='Adam';" -c 100 -i 100
Enter password:
Benchmark
Average number of seconds to run all queries: 0.995 seconds
Minimum number of seconds to run all queries: 0.876 seconds
Maximum number of seconds to run all queries: 1.155 seconds
Number of clients running queries: 100
Average number of queries per client: 1

#mysqlslap -uroot -p  --auto-generate-sql --concurrency=50,100 --number-of-queries=1000  -i 5  --debug-info
Enter password:
Benchmark
Average number of seconds to run all queries: 0.148 seconds
Minimum number of seconds to run all queries: 0.148 seconds
Maximum number of seconds to run all queries: 0.148 seconds
Number of clients running queries: 50
Average number of queries per client: 20

Benchmark
Average number of seconds to run all queries: 0.143 seconds
Minimum number of seconds to run all queries: 0.143 seconds
Maximum number of seconds to run all queries: 0.143 seconds
Number of clients running queries: 100
Average number of queries per client: 10

mysqlslap -uroot -p  --auto-generate-sql --only-print

#mysqlslap -uroot -p --concurrency=50,100,200 --iterations=1 --number-int-cols=4 --number-char-cols=35 \
--auto-generate-sql --auto-generate-sql-add-autoincrement --auto-generate-sql-load-type=mixed --engine=innodb --number-of-queries=200
Enter password:
Benchmark
Running for engine innodb
Average number of seconds to run all queries: 0.042 seconds
Minimum number of seconds to run all queries: 0.042 seconds
Maximum number of seconds to run all queries: 0.042 seconds
Number of clients running queries: 50
Average number of queries per client: 4

Benchmark
Running for engine innodb
Average number of seconds to run all queries: 0.022 seconds
Minimum number of seconds to run all queries: 0.022 seconds
Maximum number of seconds to run all queries: 0.022 seconds
Number of clients running queries: 100
Average number of queries per client: 2

Benchmark
Running for engine innodb
Average number of seconds to run all queries: 0.515 seconds
Minimum number of seconds to run all queries: 0.515 seconds
Maximum number of seconds to run all queries: 0.515 seconds
Number of clients running queries: 200
Average number of queries per client: 1

#mysqlslap -uroot -p --delimiter=";" --create="CREATE TABLE a (b int);INSERT INTO a VALUES (23)" --query="SELECT * FROM a" --concurrency=50 --iterations=200
Enter password:
Benchmark
Average number of seconds to run all queries: 0.002 seconds
Minimum number of seconds to run all queries: 0.002 seconds
Maximum number of seconds to run all queries: 0.007 seconds
Number of clients running queries: 50
Average number of queries per client: 1

mysqlslap --concurrency=5 --iterations=5 --query=query.sql --create=create.sql --delimiter=";"

参考：https://my.oschina.net/moooofly/blog/152547

where、order by、group by、表连接都会使用到索引  
主键的选择：
1、唯一非空
2、尽量的小，因为所有的二级索引都会存储主键
3、选择一个单调自增的键，物理行是按照主键排序的

alter table employees add [unqiue] index idx_name(first_name(10));
alter table employees drop index idx_name;

对于以上关于MySQL8的数据库优化讲义，如果大家还有更多需要了解的可以持续关注我们创新互联的行业推新，如需获取专业解答，可在官网联系售前售后的，希望该文章可给大家带来一定的知识更新。

 

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