openGauss每日一练打卡第18天 | openGauss视图管理

学习目标

掌握openGauss视图的管理：创建视图、删除视图、查询视图的信息、修改视图的信息。

课程学习

1.创建视图

--创建模式、表和插入数据
su - omm
sql -r

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');
--创建视图
CREATE VIEW tpcds.customer_details_view_v1 AS
SELECT * FROM tpcds.customer
WHERE c_customer_sk > 5400;
--查看视图内容
select * from tpcds.customer_details_view_v1;
 c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          6885 | 1             | Joes         | Hunter  
          9527 | 3             | James        | Cook    
          9500 | 4             | Lucy         | Baker   
(3 rows)

2.基于视图建立新的视图

create  VIEW tpcds.part_view as  SELECT * FROM  tpcds.customer_details_view_v1 where  c_customer_sk =9527;
 --查看新的视图
select * from tpcds.part_view;
 c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          9527 | 3             | James        | Cook    
(1 row)

3.创建物化视图

普通视图在查询中是实时进行计算的。如果建立视图的基表数据很多，使用视图的时候，进行实时计算视图表示的结果集，将消耗很大的计算机资源，并且费时很长。
物化视图提前计算出视图的结果集，并将该结果集保存在数据库里。
如果更新了基表,物化视图将过期。也就是说，基表更新后，物化视图不能反映最新的数据情况。因此在基表发生变化的时候，需要对物化视图进行更新。

--创建基表
drop materialized view if exists mv_test;
drop table if exists test;
create table test(id serial primary key,testnum serial);
insert into test(testnum) values(generate_series(1,100000));
omm=# insert into test(testnum) values(generate_series(1,100000));
INSERT 0 100000

--创建物化视图：
omm=# create materialized view mv_test as select * from test where testnum%2=0;
omm=# CREATE MATERIALIZED VIEW

--查看物化视图目前有多少行记录：
omm=# select count(*) from mv_test;
 count 
-------
 50000
(1 row)

4.普通视图相关的系统表pg_views

--系统视图pg_views
 schemaname |         viewname         | viewowner |                                              definition                  
                            
------------+--------------------------+-----------+------------------------------------------------------------------------------------------------------
 tpcds      | customer_details_view_v1 | omm       | SELECT  * FROM tpcds.customer WHERE (customer.c_customer_sk > 5400);
 tpcds      | part_view                | omm       | SELECT  * FROM tpcds.customer_details_view_v1 WHERE (customer_details_view_v1.c_customer_sk = 9527);
(2 rows)

5.物化视图相关的系统表GS_MATVIEW
--GS_MATVIEW系统表提供了关于数据库中每一个物化视图的信息。
omm=# select * from GS_MATVIEW;
 matviewid | mapid | ivm | needrefresh | refreshtime 
-----------+-------+-----+-------------+-------------
     16442 |     0 | f   |             | 
(1 row)

6.手动更新物化视图

--向基表test插入数据，查看物化视图有多少行记录：

omm=# insert into test(testnum) values(generate_series(1,100000));
INSERT 0 100000
omm=# select count(*) from mv_test ;
 count 
-------
 50000
(1 row)

--手动更新物化视图，并查看更新物化视图后，物化视图有多少行记录：
omm=#   refresh materialized view mv_test;
REFRESH MATERIALIZED VIEW
omm=#  select count(*) from mv_test;
 count  
--------
 100000
(1 row)

7.删除视图

--删除普通视图
omm=# DROP view tpcds.part_view;    
DROP VIEW

omm=# drop view tpcds.customer_details_view_v1 ;
DROP VIEW

--删除物化视图
omm=# drop materialized view mv_test ;
DROP MATERIALIZED VIEW

课程作业

1.创建表，创建普通视图

create table zhao(id intger,name char(20);
insert into zhao values(1,'zhao');
omm=# create view view_zhao AS SELECT * from zhao ;
CREATE VIEW

2.使用视图创建新的视图

omm=# create view view_zhao_1 AS SELECT * from view_zhao where name='zhao';

3.创建物化视图

create materialized view mv_zhao as select * from zhao where name='zhao';

4.手动更新物化视图

refresh materialized view mv_zhao;

5.删除创建的视图

drop view view_zhao;
drop view view_zhao_1;

drop materialized view mv_zhao;