openGauess每日一练第18天 | openGauss逻辑结构：视图管理

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;

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

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    
(6899, 1, 'Joes', 'Hunter'),    
(4343, 2, 'Lily','Carter'),    
(9877, 3, 'James', 'Cook'),
(9800, 4, 'Lucy', 'Baker');

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-# (6899, 1, ‘Joes’, ‘Hunter’),
omm-# (4343, 2, ‘Lily’,‘Carter’),
omm-# (9877, 3, ‘James’, ‘Cook’),
omm-# (9800, 4, ‘Lucy’, ‘Baker’);
omm=# INSERT 0 4

–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.使用视图创建新的视图

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

–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));

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

–创建物化视图：

create materialized view mv_test as 
select * from test where testnum%2=0;

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

–查看物化视图目前有多少行记录：

select count(*) from mv_test;

omm=#
omm=# select count(*) from mv_test;
count

50000
(1 row)

4.手动更新物化视图

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

–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=# 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

–删除普通视图

DROP view tpcds.part_view;
DROP view TPCDS.customer_details_view_v1;

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

–删除物化视图

DROP MATERIALIZED VIEW mv_test;

omm=# DROP MATERIALIZED VIEW mv_test;
DROP MATERIALIZED VIEW