openGauss每日一练第18天 - 学习心得体会

课程作业

1.创建表，创建普通视图

首先创建tpcds模式，在tpcds模式中创建customer表，在tpcds.customer表中插入4条数据。
创建c_customer_sk > 5400 条件视图。最后查询验证。

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

omm=# omm-# CREATE TABLE tpcds.customer
(  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.使用视图创建新的视图

基于视图tpcds.customer_details_view_v1创建新视图tpcds.part_view，条件是c_custome =9527。
查询验证新视图tpcds.part_view和视图tpcds.customer_details_view_v1。

omm=# create  VIEW tpcds.part_view as  SELECT * FROM  tpcds.customer_details_view_v1 where  c_custome =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=# 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=# 

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。

创建表test 插入输入。
创建物化视图（materialized view）mv_test。

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));
omm=# INSERT 0 100000

omm=# omm-# create materialized view mv_test as 
select * from test where testnum%2=0;
CREATE MATERIALIZED VIEW

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

omm=# 

4.手动更新物化视图

手动更新物化视图：refresh materialized

omm=# insert into test(testnum) values(generate_series(1,1000000));
INSERT 0 1000000

omm=# select count(*) from mv_test;
omm=# -[ RECORD 1 ]
count | 50000

omm=# refresh materialized view mv_test;
REFRESH MATERIALIZED VIEW

omm=# select count(*) from mv_test;
-[ RECORD 1 ]-
count | 600000

omm=# 

5.删除创建的视图

删除物化视图时要增加：MATERIALIZED 

 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=#