openGauss每日一练第18天 | 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。

1.创建表，创建普通视图

--创建模式、表和插入数据
su - omm
omm@modb:~$ gsql -r 
gsql ((openGauss 3.0.0 build 02c14696) compiled at 2022-04-01 18:12:00 commit 0 last mr  )
Non-SSL connection (SSL connection is recommended when requiring high-security)
Type "help" for help.

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
omm=# insert into tpcds.customer values (6885,1,'Joes','Hunter'),(4321,2,'Lily','Carter'),(9527,3,'James','Cook'),(9500,4,'Lucy','Baker');
omm=# 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)

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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

 --查看新的视图
omm=# select * from tpcds.part_view;
(1 row)

omm=#  c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          9527 | 3             | James        | Cook    

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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
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

--创建物化视图：
omm=# create materialized view mv_test as select * from test where testnum%2=0;
CREATE MATERIALIZED VIEW
omm=# select count(*) from test where testnum%2=0;
 count 
-------
 50000
(1 row)

--查看物化视图目前有多少行记录：
omm=# select count(*) from mv_test;
 count 
-------
 50000
(1 row)
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4.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)

omm=# select * from gs_matviews;
 schemaname | matviewname | matviewowner | tablespace | hasindexes |                     defin
ition                      
------------+-------------+--------------+------------+------------+--------------------------
---------------------------
 public     | mv_test     | omm          |            | f          | SELECT  * FROM test WHERE
 ((test.testnum % 2) = 0);
(1 row)

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5.删除创建的视图

--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
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