MySQL 5.7 在初始安裝後（CentOS7 作業系統）會生成隨機初始密碼，並在 /var/log/mysqld.log 中有記錄，可以通過 cat 命令檢視，找 password 關鍵字

mysql賬號許可權新增：

mysql -uroot -p
mysql>insert into mysql.user(Host,User,Password) values('%', 'userrw', password('userrw'));
mysql>flush privileges;
mysql>grant all  on *.* to 'userrw'@'%' identified by 'userrw';   #賦予全部許可權
mysql>grant select,insert,update,delete,create,drop,index,alter,grant,references,reload,shutdown,process,file on *.* to 'userrw'@'%' identified by 'userrw';
mysql>flush privileges;
 
       #mysql 5.7以上版本新增mysql.user賬號方法（password欄位改為了authentication_string）：

        CREATE USER 'user'@'localhost' IDENTIFIED BY 'userrw';
        CREATE USER 'userro'@'localhost' IDENTIFIED BY 'userro';
        grant all privileges on db.* to 'userrw'@'localhost';
        grant all privileges on db.* to 'userro'@'localhost';

mysql非常有用的常用操作：
a、匯出資料庫(沒有資料)
mysqldump -uroot -p123456 --opt --add-drop-table --add-drop-database -d -B db >db.nodata.sql   //-d no data;
mysqldump -uroot -p123456 --opt --add-drop-table --add-drop-database -B db >db.sql  //struct and data
b、查詢資料庫中記錄不為空的表
use information_schema;
select * from TABLES where TABLE_ROWS>0 AND TABLE_SCHEMA='db';
mysqldump -uroot -p123456  db version >db-version.sql    //匯出db資料庫version表的結構和資料
        d、ｍｙｓｑｌ跨庫查詢(連庫查詢)
                select subscriber.username,subscriber.password, member.email from db.subscriber,db2.member where subscriber.username=member.id and member.book_id='193' limit 20;
                select subscriber.username,subscriber.password, member.email,member.book_id from db.subscriber,db2.member where subscriber.username=member.id and member.book_id='193';