openGauss每日一练第18天 | 学习心得体会

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;

******************
omm=# omm-# CREATE VIEW tpcds.customer_details_view_v1 AS
SELECT * FROM tpcds.customer
omm-# WHERE c_customer_sk > 5400;
CREATE VIEW
omm=# 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)
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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;

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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));

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

--查看物化视图目前有多少行记录：
select count(*) from mv_test;

**************
omm=# select count(*) from mv_test;
 count 
-------
 50000
(1 row)
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4.普通视图相关的系统表pg_views

select * from pg_views where schemaname = 'tpcds' or schemaname = 'public';
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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。
select * from GS_MATVIEW;

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6.手动更新物化视图

insert into test(testnum) values(generate_series(1,100000));
select count(*) from mv_test;

*********************

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


omm=# select count(*) from test;
 count  
--------
 200000
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5.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：

refresh materialized view mv_test;
 select count(*) from mv_test;

************
omm=#  select count(*) from mv_test;
 count  
--------
 100000
(1 row)
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7.删除视图

--删除普通视图
DROP view tpcds.part_view;
DROP view TPCDS.customer_details_view_v1;

--删除物化视图
DROP MATERIALIZED VIEW mv_test;

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课程作业

 1.创建表，创建普通视图
Create schema scuser;
CREATE TABLE scuser.user1
(  id             integer,   
  age             char(5),    
  name              char(6)
) ;
INSERT INTO scuser.user1 VALUES    
(6885, 18, 'Joes'),    
(4321, 20, 'Lily'),    
(9527, 23, 'James'),
(9500, 24, 'Lucy');

--创建视图
CREATE VIEW scuser.user1_view_v1 AS
SELECT * FROM scuser.user1
WHERE id > 5400;
2.使用视图创建新的视图
create  VIEW scuser.part_view  as  SELECT * FROM scuser.user1_view_v1 where  id =9527;
3.创建物化视图
create materialized view mv_user1_ld as  select * from scuser.user1;
4.手动更新物化视图
refresh materialized view mv_user1_ld;
5.删除创建的视图
DROP view scuser.user1_view_v1;
DROP view scuser.part_view;
--删除物化视图
DROP MATERIALIZED VIEW mv_user1_ld;
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