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;

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=# CREATE VIEW tpcds.customer_details_view_v1 AS
omm-# 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)

omm=# 

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;

omm=# create  VIEW tpcds.part_view as  SELECT * FROM  tpcds.customer_details_view_v1 where  c_customer_sk =9527;
CREATE VIEW
omm=# select * from tpcds.part_view;
 c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          9527 | 3             | James        | Cook    
(1 row)

omm=# 

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

omm=#

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';

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)

omm=#

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;

omm=# select * from GS_MATVIEW;
 matviewid | mapid | ivm | needrefresh | refreshtime 
-----------+-------+-----+-------------+-------------
     16412 |     0 | f   |             | 
(1 row)

omm=#

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;

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

omm=#   refresh materialized view mv_test;
REFRESH MATERIALIZED VIEW
omm=#  select count(*) from mv_test;
 count  
--------
 100000
(1 row)

omm=#

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;

omm=# DROP view tpcds.part_view;
DROP VIEW
omm=# DROP view TPCDS.customer_details_view_v1;
DROP VIEW
omm=# DROP MATERIALIZED VIEW mv_test;
DROP MATERIALIZED VIEW
omm=# 

课程作业

1.创建表，创建普通视图

create table txiaocx(id int,name varchar(20));
insert into txiaocx(name) values('user1');
insert into txiaocx(name) values('user2');
insert into txiaocx(name) values('user3');
insert into txiaocx(name) values('user4');
insert into txiaocx(name) values('user5');
insert into txiaocx(name) values('user6');
insert into txiaocx(name) values('xiaocx1');
insert into txiaocx(name) values('xiaocx2');
insert into txiaocx(name) values('xiaocx3');

omm=# create table txiaocx(id int,name varchar(20));
CREATE TABLE
omm=# insert into txiaocx(name) values('user1');
INSERT 0 1
omm=# insert into txiaocx(name) values('user2');
INSERT 0 1
omm=# insert into txiaocx(name) values('user3');
INSERT 0 1
omm=# insert into txiaocx(name) values('user4');
INSERT 0 1
omm=# insert into txiaocx(name) values('user5');
INSERT 0 1
omm=# insert into txiaocx(name) values('user6');
INSERT 0 1
omm=# insert into txiaocx(name) values('xiaocx1');
INSERT 0 1
omm=# insert into txiaocx(name) values('xiaocx2');
INSERT 0 1
omm=# insert into txiaocx(name) values('xiaocx3');
INSERT 0 1
omm=# 

2.使用视图创建新的视图

CREATE VIEW v_xiaocx AS SELECT * FROM txiaocx WHERE name like 'xiaocx%';

select * from v_xiaocx;

\dv
CREATE VIEW v_xiaocx_01 AS SELECT * from v_xiaocx;

select * from v_xiaocx;
\dv

omm=# CREATE VIEW v_xiaocx AS SELECT * FROM txiaocx WHERE name like 'xiaocx%';
CREATE VIEW
omm=# 
omm=# select * from v_xiaocx;
 id |  name   
----+---------
    | xiaocx1
    | xiaocx2
    | xiaocx3
(3 rows)

omm=#omm=# \dv
             List of relations
 Schema |   Name   | Type | Owner | Storage 
--------+----------+------+-------+---------
 public | v_xiaocx | view | omm   | 
(1 row)

omm=#
omm=# CREATE VIEW v_xiaocx_01 AS SELECT * from v_xiaocx;
CREATE VIEW
omm=# 
omm=# select * from v_xiaocx_01;
 id |  name   
----+---------
    | xiaocx1
    | xiaocx2
    | xiaocx3
(3 rows)

omm=# \dv
               List of relations
 Schema |    Name     | Type | Owner | Storage 
--------+-------------+------+-------+---------
 public | v_xiaocx    | view | omm   | 
 public | v_xiaocx_01 | view | omm   | 
(2 rows)

omm=# 

3.创建物化视图

insert into txiaocx(name) values(generate_series(1,100000));

create materialized view mv_xiaocx as select * from txiaocx where name>'5000';

select count(*) from mv_xiaocx;

\dm

omm=# insert into txiaocx(name) values(generate_series(1,100000));
INSERT 0 100000
omm=#
omm=# create materialized view mv_xiaocx as select * from txiaocx where name>'5000';
CREATE MATERIALIZED VIEW
omm=# select count(*) from mv_xiaocx;
 count 
-------
 55560
(1 row)

omm=# \mv
Invalid command \mv. Try \? for help.
omm=# \dmv
                                  List of relations
 Schema |    Name     |       Type        | Owner |             Storage              
--------+-------------+-------------------+-------+----------------------------------
 public | mv_xiaocx   | materialized view | omm   | {orientation=row,compression=no}
 public | v_xiaocx    | view              | omm   | 
 public | v_xiaocx_01 | view              | omm   | 
(3 rows)

omm=# \dm
                                 List of relations
 Schema |   Name    |       Type        | Owner |             Storage              
--------+-----------+-------------------+-------+----------------------------------
 public | mv_xiaocx | materialized view | omm   | {orientation=row,compression=no}
(1 row)

omm=# 

4.手动更新物化视图

insert into txiaocx(name) values(generate_series(1,100000));
select count(*) from mv_xiaocx;
refresh materialized view mv_xiaocx;
select count(*) from mv_xiaocx;

omm=# insert into txiaocx(name) values(generate_series(1,100000));
INSERT 0 100000
omm=# select count(*) from mv_xiaocx;
 count 
-------
 55560
(1 row)

omm=# refresh materialized view mv_xiaocx;
REFRESH MATERIALIZED VIEW
omm=# select count(*) from mv_xiaocx;
 count  
--------
 111111
(1 row)

omm=#

5.删除创建的视图

\dmv

DROP VIEW v_xiaocx_01;
DROP VIEW v_xiaocx;
DROP MATERIALIZED VIEW mv_xiaocx;
\dmv

注意这里在删除视图（v_xiaocx），需要先删除依赖该视图的对象（v_xiaocx_01），或者使用关键字CASCADE。

DROP VIEW v_xiaocx CASCADE;

\dv

omm=# \dmv
                                  List of relations
 Schema |    Name     |       Type        | Owner |             Storage              
--------+-------------+-------------------+-------+----------------------------------
 public | mv_xiaocx   | materialized view | omm   | {orientation=row,compression=no}
 public | v_xiaocx    | view              | omm   | 
 public | v_xiaocx_01 | view              | omm   | 
(3 rows)

omm=#
omm=# DROP view v_xiaocx;
ERROR:  cannot drop view v_xiaocx because other objects depend on it
DETAIL:  view v_xiaocx_01 depends on view v_xiaocx
HINT:  Use DROP ... CASCADE to drop the dependent objects too.omm=# DROP view v_xiaocx_01;
DROP VIEWomm=# DROP view v_xiaocx;
DROP VIEW
omm=# DROP MATERIALIZED VIEW mv_xiaocx;
DROP MATERIALIZED VIEW
omm=# 
omm=# DROP VIEW v_xiaocx CASCADE;
NOTICE:  drop cascades to view v_xiaocx_01
DROP VIEW
omm=# \DV
Invalid command \DV. Try \? for help.
omm=# \dv
No relations found.
omm=# 
omm=# \dmv
No relations found.
omm=#