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
gsql -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

#创建模式，表，并插入数据
enmdb=# create schema tpcds;
CREATE SCHEMA
enmdb=# create table tpcds.customer( 
enmdb(# c_customer_sk integer,
enmdb(# c_customer_id  char(5),
enmdb(# c_first_name   char(6),
enmdb(# c_last_name    char(8)
enmdb(# );
CREATE TABLE

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

#创建视图
enmdb=# create view tpcds.customer_details_view_v1 as
enmdb-# select * from tpcds.customer
enmdb-# where c_customer_sk > 5400;
CREATE VIEW

#使用视图
enmdb=# 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. 使用视图创建新的视图

enmdb=# create view tpcds.part_view as
enmdb-# select * from tpcds.customer_details_view_v1
enmdb-# where c_customer_sk=9527;
CREATE VIEW

enmdb=# select * from tpcds.part_view;
 c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          9527 | 3             | James        | Cook    
(1 row)

#与普通视图有关的系统表查询
enmdb=# select * from pg_views where schemaname='tpcds' or schemaname='public';

enmdb=#  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)

3. 创建物化视图

#创建基表，并插入数据
enmdb=# 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
enmdb=# 
enmdb=# insert into test(testnum) values(generate_series(1,100000));
INSERT 0 100000

#创建物化视图（这里视图定义的条件是：存放偶数列）
enmdb=# create materialized view mv_test as
enmdb-# select * from test where testnum%2=0;
CREATE MATERIALIZED VIEW

#查询目前物化视图与基表的数据量对比
enmdb=# select count(*) from test;
(1 row)

enmdb=#  count  
--------
 100000

enmdb=# select count(*) from mv_test;
enmdb=#  count 
-------
 50000
(1 row)

#与物化视图有关的系统表
enmdb=# select * from gs_matview;
 matviewid | mapid | ivm | needrefresh | refreshtime 
-----------+-------+-----+-------------+-------------
     16755 |     0 | f   |             | 
(1 row)

4. 手动更新物化视图

#向基表test插入数据
enmdb=# insert into test(testnum) values(generate_series(1,100000));
INSERT 0 100000

#查看基表与物化视图数据量的对比
enmdb=# select count(*) from test;
 count  
--------
 200000
(1 row)

enmdb=# select count(*) from mv_test;
 count 
-------
 50000
(1 row)

#手工刷新物化视图
enmdb=# refresh materialized view mv_test;
REFRESH MATERIALIZED VIEW

#刷新后，再次查询物化视图的数据量，发现变化了
enmdb=# select count(*) from mv_test;
 count  
--------
 100000
(1 row)

5. 删除创建的视图

删除基于视图的视图时，需要注意删除视图的顺序。比如下面先删除基视图时，就会报错

enmdb=# drop view tpcds.customer_details_view_v1;
enmdb=# ERROR:  cannot drop view tpcds.customer_details_view_v1 because other objects depend on it
DETAIL:  view tpcds.part_view depends on view tpcds.customer_details_view_v1
HINT:  Use DROP ... CASCADE to drop the dependent objects too.

#删除普通视图
enmdb=# drop view tpcds.part_view;
DROP VIEW
enmdb=# drop view tpcds.customer_details_view_v1;
DROP VIEW

#删除物化视图
enmdb=# drop materialized view mv_test;
DROP MATERIALIZED VIEW