view
** The view is a virtual table whose content is defined by the query. ** Like a real table, the view contains a series of named columns and rows of data. The data changes
of the view will affect the base table, and the data changes of the base table will also affect the view.
Basic use
Create a view
create view view name as select statement; // When querying ~~, create a view
select * from v_ename_dname;
Modified the view, which affects the base table data.
Modified the base table, which affects the view.
update v_ename_dname set dname='sales' where ename='CLARK';
select * from EMP where ename='CLARK';
Delete view
drop view view name;
View rules and restrictions
As with tables, they must be uniquely named (views or table names with the same name cannot appear) The number of views created is unlimited, but the performance impact after creating a complex query as a view must be considered
The view cannot add an index , nor can it have associated triggers or the default value view can improve security, and must have sufficient access rights
** order by can be used in the view, ** but if you retrieve data from the view, select also contains order by, then the order by in this view will be overwritten. The view can be used with tables
User Management
If we can only use the root user, there is a security risk. At this time, you need to use MySQL user management.
user
1 User information
Users in MySQL are stored in the user table of the system database mysql
select host,user,authentication_string from user;
Field explanation:
host: indicates from which host this user can log in, if it is localhost, it can only log in from this machine user: user name
authentication_string: user password encrypted by password function
* _priv: user-owned permissions
Create user syntax:
create user 'user name' @ 'login host / ip' identified by 'password';
create user 'litao'@'localhost' identified by '123456';
select host,user, password from user where user='litao';
3 Delete user
Syntax:
drop user 'user name' @ 'hostname' Example:
Modify user password syntax:
1 Change your own password
set password = password ('new password');
** 2 root users modify the password of the specified user **
set password for 'user name' @ 'host name' = password ('new password');
set password for 'litao' @ 'localhost' = password ('abcdefg' );
Database permissions
List of permissions provided by MySQL database:
**
1 Authorize users
The user just created does not have any permissions. Need to authorize the user. **
Syntax:
grant permission list on library. Object name to 'user name' @ 'login location' [identified by 'password']
Description: permission list, multiple permissions are separated by commas
Permission list, multiple permissions are separated by commas
grant select on…
grant select, delete, create on…
grant all [privileges] on… – means to grant the user all the permissions on the object
On behalf of the system. "" All in all objects in the database (tables, views, stored procedures, etc.)
library : indicates that a database of all * data objects (tables, views, stored procedures, etc.)
IDENTIFIED by optional. If the user exists, change the password while granting the permission, if the user does not exist, it is to create a user
-- root 给 litao 赋予账户查询mytest库的DEPT表的权限
mysql> grant select on mytest.DEPT to 'litao'@'localhost';
show databases;
-- litao账户可以看到mytest库
Note: If it is found that the authorization is not effective, execute the following instructions:
flush privileges;
2 Recycling authority
Syntax:
revoke permission list on library. Object name from 'user name' @ 'login location'; Example:
-- 回收litao对数据库的所有权限
revoke all on mytest.DEPT from 'litao'@'localhost';
