Use of views

Concept

The view is a virtual table , It preserves SELECT The definition of the statement , It is a way for users to view data in data .
Through it, you can browse part or all of the data in the table in the way you need , And these data are still stored in the table of the database , Such a table is called a base table .

characteristic

• The data in the view does not belong to the view itself , It's a basic table , Views can be treated like tables insert,update,delete operation .

• The view cannot be modified , After the table is modified or deleted, the view should be deleted and rebuilt .

• There is no limit to the number of views , But names can't be repeated with views and tables , Have uniqueness .

• Views can be nested , One view can be nested with another view .

• View cannot be indexed , Cannot have an associated trigger and default value ,sql server Cannot be used after a view order by Sort .

Create and use views

• Create view
  create view view_name as select_statement( Some operations of adding, deleting, modifying and querying tables )
  • eg:
    create name v_student as select * from student where stuno=“20000002”
• View view
  select * from v_student;
• Modify the view
  alter view view_name as select_statement
  • eg:
    alter view v_student as select stuname,stuno from student where class=‘002’;
• Delete view
  drop view view_name;
  • eg:
    drop view v_student;