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
root@modb:~# 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

<<创建表
CREATE TABLE tpcds.customer
(  c_customer_sk             integer,   
  c_customer_id             char(5),    
  c_first_name              char(6),    
  c_last_name               char(8) 
) ;
创建表

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

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

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


--创建视图

<<创建视图
CREATE VIEW tpcds.customer_details_view_v1 AS
SELECT * FROM tpcds.customer
WHERE c_customer_sk > 5400;
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

--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)

2.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 
---------------+---------------+--------------+-------------
omm=#           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

<<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));
创建基表

omm=# drop materialized view if exists mv_test;
WARNING:  Session unused timeout.
FATAL:  terminating connection due to administrator command
could not send data to server: Broken pipe
The connection to the server was lost. Attempting reset: Succeeded.
omm=# 
omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
omm=# omm=# 

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=# 
omm=# insert into test(testnum) values(generate_series(1,100000));

INSERT 0 100000

--创建物化视图：

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

omm=# create materialized view mv_test as 
omm-# 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;
omm=#  count 
-------
 50000
(1 row)

4.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)

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 
-----------+-------+-----+-------------+-------------
     16412 |     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=# omm=# 

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=# 
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