openGauss每日一练第18天-随堂笔记

1. 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。

2. 课程学习

• 创建视图

--创建模式、表和插入数据
su - omm
sql -r

omm=# Create schema tpcds;
CREATE SCHEMA
omm=# CREATE TABLE tpcds.customer
 (  c_customer_sk             integer,   
   c_customer_id             char(5),    
   c_first_name              char(6),    
   c_last_name               char(8) 
  ) ;
CREATE TABLE

INSERT INTO tpcds.customer VALUES    
(6885, 1, 'Joes', 'Hunter'),    
(4321, 2, 'Lily','Carter'),    
(9527, 3, 'James', 'Cook'),
(9500, 4, 'Lucy', 'Baker');
INSERT 0 4

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

--查看视图内容
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)

• 基于视图建立新的视图

omm=# create  VIEW tpcds.part_view as  SELECT * FROM  tpcds.customer_details_view_v1 where  c_customer_sk =9527;
CREATE VIEW

 --查看新的视图
omm=# select * from tpcds.part_view;
 c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          9527 | 3             | James        | Cook    
(1 row)

• 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
omm=# drop materialized view if exists mv_test;
NOTICE:  materialized view "mv_test" does not exist, skipping
DROP MATERIALIZED VIEW
omm=# drop table if exists test;
DROP TABLE

omm=# create table test(id serial primary key,testnum serial);
NOTICE:  CREATE TABLE will create implicit sequence "test_id_seq" for serial column "test.id"
NOTICE:  CREATE TABLE will create implicit sequence "test_testnum_seq" for serial column "test.testnum"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
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;
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)

• 普通视图相关的系统表pg_views

--系统视图pg_views
omm=# select * from pg_views where schemaname = 'tpcds' or schemaname = 'public';
 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)

• 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 
-----------+-------+-----+-------------+-------------
     16552 |     0 | f   |             | 
(1 row)

• 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)

• 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

3. 总结
   本节课学习了视图、物化视图相关的操作和维护步骤。