mysql5.7 误删管理员root帐户

1.中止数据库，并在mysql配置文件my.cnf中添加skip-grant-tables参数到[mysqld]配置块中

2. 执行 systemctl start mysqld

3. 执行 mysql 

4.建立 root 用户并赋权限，并修改root密码

insert into user set user='root',ssl_cipher='',x509_issuer='',x509_subject='';

update user set Host='localhost',select_priv='y', insert_priv='y',update_priv='y', Alter_priv='y',delete_priv='y',create_priv='y',drop_priv='y',reload_priv='y',shutdown_priv='y',Process_priv='y',file_priv='y',grant_priv='y',References_priv='y',index_priv='y',create_user_priv='y',show_db_priv='y',super_priv='y',create_tmp_table_priv='y',Lock_tables_priv='y',execute_priv='y',repl_slave_priv='y',repl_client_priv='y',create_view_priv='y',show_view_priv='y',create_routine_priv='y',alter_routine_priv='y',create_user_priv='y' where user='root';

update user set authentication_string=password('123456') where user='root';

5. 刷新 退出mysql

flush privileges;
quit

6.注释掉skip-grant-tables参数，重启数据库