openGauss每日一练第18天

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。

课程作业

1.创建表，创建普通视图

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=# 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');
INSERT 0 4
omm=# CREATE VIEW tpcds.customer_details_view_v1 AS
SELECT * FROM tpcds.customer
 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)

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

omm=# select * from tpcds.part_view;
 c_customer_sk | c_customer_id | c_first_name | c_last_name 
---------------+---------------+--------------+-------------
          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。

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;
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)

4.手动更新物化视图

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)

5.删除创建的视图

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