原创 openGauss每日一练第18天 | 3.0.0学习心得体会

原创手机用户6637 2022-12-11

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第十八课

18.1 第18天 | openGauss逻辑结构：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;

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;
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;

4.普通视图相关的系统表pg_views

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

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;
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：

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

–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;
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;

课程作业

1.创建表，创建普通视图


omm=# Create schema tpcds;
CREATE SCHEMA
omm=# CREATE TABLE tpcds.customer
omm-# (  c_customer_sk             integer,   
omm(#   c_customer_id             char(5),    
omm(#   c_first_name              char(6),    
omm(#   c_last_name               char(8) 
omm(# ) ;
CREATE TABLE
omm=# INSERT INTO tpcds.customer VALUES    
omm-# (6885, 1, 'Joes', 'Hunter'),    
omm-# (4321, 2, 'Lily','Carter'),    
omm-# (9527, 3, 'James', 'Cook'),
omm-# (9500, 4, 'Lucy', 'Baker');
INSERT 0 4
omm=# --创建视图
omm=# CREATE VIEW tpcds.customer_details_view_v1 AS
omm-# SELECT * FROM tpcds.customer
omm-# WHERE c_customer_sk > 5400;
CREATE VIEW
omm=# --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)

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2.使用视图创建新的视图


omm=# create  VIEW tpcds.part_view as  SELECT * FROM  tpcds.customer_details_view_v1 where  c_customer_sk =9527;
CREATE VIEW
omm=#  --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)
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3.创建物化视图


omm=# --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;
NOTICE:  table "test" does not exist, skipping
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
omm=# 
omm=# --创建物化视图：
omm=# create materialized view mv_test as 
omm-# select * from test where testnum%2=0;
CREATE MATERIALIZED VIEW
omm=# 
omm=# --查看物化视图目前有多少行记录：
omm=# select count(*) from mv_test;
 count 
-------
 50000
(1 row)

omm=# --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 (custome
r.c_customer_sk > 5400);
 tpcds      | part_view                | omm       | SELECT  * FROM tpcds.customer_details_view_v
1 WHERE (customer_details_view_v1.c_customer_sk = 9527);
(2 rows)

omm=# select * from 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=# 
 matviewid | mapid | ivm | needrefresh | refreshtime 
-----------+-------+-----+-------------+-------------
     16413 |     0 | f   |             | 
(1 row)

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4.手动更新物化视图



omm=# omm=# --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)

omm=# 
：=# --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)

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5.删除创建的视图


omm=# --删除普通视图
omm=# DROP view tpcds.part_view;
DROP VIEW
omm=# DROP view TPCDS.customer_details_view_v1;
DROP VIEW
omm=# 
omm=# --删除物化视图
omm=# DROP MATERIALIZED VIEW mv_test;
DROP MATERIALIZED VIEW
omm=# 
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