Database Views principle of system (e)

Database Views principle of system (e)

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View of the advantages and disadvantages

Advantages:

1. 集中分散数据
2. 简化查询语句
3. 重用SQL语句
4. 保护数据安全
5. 共享所需数据
6. 更改数据格式

Disadvantages:

    1. 性能差
    2. 修改限制

Create a view

Create view view_name[(column_name)] -- 为每个列指定名称
    as select_statement -- 指定select语句
    [WITH [CASCADED | LOCAL] CHECK OPTION] -- 可选项，指定在可更新视图上所进行的修改都需要符合select_statement中所指定的限制条件

-- 创建视图students_view,包含所有男同学的所有信息，并且在基表修改的时候视图跟着改变
CREATE OR REPLACE view students_view 
as select * from students where sex=1
with check option 

Delete View

DROP view [if exists] view_name[,view_name1...]
-- 删除视图
deop view if exists students_view

Modify View

-- 和创建视图一样，只是所用关键字不同
ALTER  VIEW view_name [(column_list)]
      AS select_statement
      [WITH [CASCADED | LOCAL]CHECK OPTION]

View View

-- 查看视图的结构
SHOW　CREATE　view　view_name

Update View data

-- 查看视图数据
select * from students_view
-- 插入视图数据
insert into students_view VALUES (4,"wang",1,12,2)
-- 更新视图数据
UPDATE students_view set name="SUnArmy" WHERE id=4
-- 删除视图数据
DELETE FROM students_view WHERE name="SunArmy"