第十一天

11.1 打卡第11天| 学习openGauss视图

学习目标

学习openGauss视图

视图与基本表不同，是一个虚拟的表。数据库中仅存放视图的定义，而不存放视图对应的数据，这些数据仍存放在原来的基本表中。

课程学习

连接openGauss

#第一次进入等待15秒
#数据库启动中...
su - omm
gsql -r

1.创建视图

–为系统表pg_tablespace创建字段spcname为pg_default组成的视图
CREATE VIEW tps_view AS
SELECT * FROM pg_tablespace WHERE spcname = 'pg_default';

–查看视图
SELECT * FROM tps_view ;

–创建一个由c_customer_sk小于6000的内容组成的视图
Create schema tpcds;
CREATE TABLE tpcds.customer
(  c_customer_sk             integer,   
  c_customer_id             char(5),    
  c_first_name              char(6),    
  c_last_name               char(8) 
) ;
INSERT INTO tpcds.customer VALUES    
(6885, 1, 'Joes', 'Hunter'),    
(4321, 2, 'Lily','Carter'),    
(9527, 3, 'James', 'Cook'),
(9500, 4, 'Lucy', 'Baker');
CREATE VIEW tpcds.customer_details_view_v1 AS
SELECT * FROM tpcds.customer
WHERE c_customer_sk < 6000;

–查看视图
select * from tpcds.customer_details_view_v1;

–系统视图
select * from pg_views where schemaname = 'tpcds' or schemaname = 'public';

2.修改视图定义

–修改视图名称
ALTER VIEW tpcds.customer_details_view_v1 RENAME TO customer_details_view_v2;

–修改视图所属schema
ALTER VIEW tpcds.customer_details_view_v2 SET schema public;

–修改视图owner
create user jack password 'abcd@123';
alter view tps_view owner to jack;

–查看系统视图tps_views
select * from pg_views where viewname = 'customer_details_view_v2' or viewname = 'tps_view';

3.删除视图

DROP VIEW customer_details_view_v2;
Drop view tps_view;

课程作业

1.为系统表PG_DATABASE创建视图，重命名视图并修改owner为jim,

create view db_view as select * from pg_database;
alter view db_view rename to db_view2;
create user jim password 'gauss_4U';
alter view db_view2 owner to jim;
select * from pg_views where viewname='db_view2';
\dv

2.创建一个用户表student，并在用户表上创建视图，修改视图schema;

create table student (
id int,
first_name char(20),
last_name char(20)
);

insert into student values
(1, 'Joes', 'Hunter'),
(2, 'Lily','Carter'),
(3, 'James', 'Cook'),
(4, 'Lucy', 'Baker');

create view student_view as select * from student where id>2;
create schema school;
select * from student_view;
alter view student set schema school;
\dv
\dv school.*

3.使用pg_views查看视图信息

select * from pg_views where viewname='db_view2' or viewname='student_view';

4.删除视图、表、用户

drop view db_view2;
drop view school.student_view;
drop table student;
drop user jim cascade;
drop schema school;