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;
