Understand mysql_ commonly used classic sql

1. Allow mysql remote connection
      as in 4

    3. View character set settings
       show variables like 'character%';

    4. Database

      grant grant all on *.* to 'root'@'%' identified by 'Reset123QWE';
      flush privileges;

      grant permission name (all permissions are used) on library name (*all). Table name (*all) to 'username to be authorized'@'%'(% means all IPs, you can only add one IP)
    
      grant USAGE on cms.* to testread@'%' identified by '123456';
      grant select on cms.* to testread@'%' identified by '123456';
      grant all on test.* to 'testread'@'%' identified by '123456';

     5. Modify mysql password
      >use mysql
      >update user set password=PASSWORD('Reset123QWE') where user='root'
      >flush privileges

6. Look at the current default storage engine of your mysql:
        mysql> show variables like '%storage_engine%';

7. See what storage engine your mysql now provides:
       mysql> show engines;

8. View the current isolation level
      SELECT @@tx_isolation;

9. Set the global transaction isolation level
      set global transaction isolation level read committed;
          set session transaction isolation level read committed;

     10. Export mysql
        mysqldump -uroot -pReset123QWE --all-databases > cms.sql

11. View the current connection number configuration
     show variables like 'max_connections';

12. Set the maximum connection Number
     set global max_connections=1000;

  13. Modify my.cnf, configure the maximum number of connections
    max_connections=2000

14. Get the date of the previous day
   select date_sub(curdate(), interval 1 day);

15. Query the date of a certain day
       SELECT * FROM tb_task_info_20160301 WHERE DATE(create_time) = '2016-03-01' ORDER BY create_time DESC

16. Query the number of records of all tables in a library
select table_name,table_rows from tables order by TABLE_ROWS desc limit 0,100

17. Forgot the password, start mysqld in another way
--defaults-file="C:\mysql-5.5.39-win32\my.ini" --console --skip-grant-tables

18. Group statistics having
   SELECT domain, COUNT(id) c FROM tb_tencent_cfg_domain GROUP BY domain HAVING(c)>1

19. Filter delete
   DELETE FROM tb_tencent_cfg_domain WHERE (`domain`, `id`) IN (
        SELECT v.domain, v.id FROM
                (SELECT domain , MAX(id) id FROM tb_tencent_cfg_domain GROUP BY domain HAVING COUNT(id)>1 ) v
    ) ;

20. Check if sql has changed
       WHERE id = #id#           
            and ifnull(date_format(modify_time,'%Y-%m-%d %H:%i:%s'),'') = ifnull(#modifyTime#,'');