一、学习目标
本节课的学习目标是学习openGauss数据库、用户和模式的关系以及访问方式，理解模式是在数据库层面、用户是在实例层面。
此处借用恩墨培训讲义的一幅讲解openGauss逻辑结构的图：
从上面这幅图，我们能看到openGauss逻辑结构中数据库、模式以及用户的关系。
- 表由多个行与列组成，被分组存储成为了数据库；
- 一个由单个openGauss服务器实例管理的数据库集合组成一个数据库集簇(Database Cluster)；
- 一个数据库集簇由多个用户(Users)和多个数据库(Databases)组成，这些数据库和用户共用同一套数据库实例以及相关配置文件。
二、测试练习
2.1 创建数据库及表空间
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=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+-------+----------+---------+-------+-------------------
omm | omm | UTF8 | C | C |
postgres | omm | UTF8 | C | C |
template0 | omm | UTF8 | C | C | =c/omm +
| | | | | omm=CTc/omm
template1 | omm | UTF8 | C | C | =c/omm +
| | | | | omm=CTc/omm
(4 rows)
omm=# CREATE TABLESPACE music_tbs RELATIVE LOCATION 'tablespace/test_ts1';
CREATE TABLESPACE
omm=# CREATE DATABASE musicdb WITH TABLESPACE = music_tbs;
CREATE DATABASE
2.2 创建用户并授权
omm=# CREATE USER user1 IDENTIFIED BY 'kunpeng@1234';
NOTICE: The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# ALTER USER user1 SYSADMIN;
ALTER ROLE
2.3 使用创建用户连接数据库
omm@modb:~$ gsql -d musicdb -U user1 -p 5432 -W kunpeng@1234 -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.
musicdb=> \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+-------+----------+---------+-------+-------------------
musicdb | omm | UTF8 | C | C |
omm | omm | UTF8 | C | C |
postgres | omm | UTF8 | C | C |
template0 | omm | UTF8 | C | C | =c/omm +
| | | | | omm=CTc/omm
template1 | omm | UTF8 | C | C | =c/omm +
| | | | | omm=CTc/omm
(5 rows)
musicdb=> List of tablespaces
Name | Owner | Location
------------+-------+---------------------
music_tbs | omm | tablespace/test_ts1
pg_default | omm | 
2.4 在musicdb库下创建四个schema
musicdb=> create schema schema2 AUTHORIZATION user1;
musicdb=> CREATE SCHEMA
musicdb=> create schema schema3 AUTHORIZATION user1;
CREATE SCHEMA
musicdb=> create schema schema4 AUTHORIZATION user1;
CREATE SCHEMA
2.5 查看musicdb库下所有模式
musicdb=> \dn
List of schemas
Name | Owner
-----------------+-------
blockchain | omm
cstore | omm
db4ai | omm
dbe_perf | omm
dbe_pldebugger | omm
dbe_pldeveloper | omm
pkg_service | omm
public | omm
schema1 | user1
schema2 | user1
schema3 | user1
schema4 | user1
schm1 | user1
snapshot | omm
sqladvisor | omm
(15 rows)
musicdb=> SELECT catalog_name, schema_name, schema_owner FROM information_schema.schemata;
catalog_name | schema_name | schema_owner
--------------+--------------------+--------------
musicdb | pg_toast | omm
musicdb | cstore | omm
musicdb | pkg_service | omm
musicdb | dbe_perf | omm
musicdb | snapshot | omm
musicdb | blockchain | omm
musicdb | pg_catalog | omm
musicdb | public | omm
musicdb | sqladvisor | omm
musicdb | dbe_pldebugger | omm
musicdb | dbe_pldeveloper | omm
musicdb | information_schema | omm
musicdb | db4ai | omm
musicdb | schm1 | user1
musicdb | schema1 | user1
musicdb | schema2 | user1
musicdb | schema3 | user1
musicdb | schema4 | user1
(18 rows)
-- 通过以上两种方式查看数据库下的所有模式，可以发现查询到信息有些差异，\dn查询到的要少一些，相比语句查询少了pg_toast、snapshot、information_schema这三个模式。 
2.6 分别在musicdb库下不同模式创建同名表并插入数据
musicdb=> create table schema1.tb01(content varchar(100));
CREATE TABLE
musicdb=> create table schema2.tb01(content varchar(100));
CREATE TABLE
musicdb=> create table schema3.tb01(content varchar(100));
CREATE TABLE
musicdb=> create table schema4.tb01(content varchar(100));
CREATE TABLE
musicdb=>
musicdb=> insert into schema1.tb01 values('This is schema1');
INSERT 0 1
musicdb=> insert into schema2.tb01 values('This is schema2');
INSERT 0 1
musicdb=> insert into schema3.tb01 values('This is schema3');
INSERT 0 1
musicdb=> insert into schema4.tb01 values('This is schema4');
INSERT 0 1
2.7 创建并查看视图
musicdb=> create or replace view show_tables as
musicdb-> select table_catalog, table_schema, table_name, table_type
musicdb-> from information_schema.tables
musicdb-> where table_schema not in ('pg_catalog', 'information_schema','dbe_perf');
CREATE VIEW
musicdb=> select * from show_tables;
table_catalog | table_schema | table_name | table_type
---------------+-----------------+-------------+------------
musicdb | db4ai | snapshot | BASE TABLE
musicdb | dbe_pldeveloper | gs_errors | BASE TABLE
musicdb | dbe_pldeveloper | gs_source | BASE TABLE
musicdb | public | show_tables | VIEW
musicdb | schema4 | tb01 | BASE TABLE
musicdb | schema3 | tb01 | BASE TABLE
musicdb | schema2 | tb01 | BASE TABLE
musicdb | schema1 | tb01 | BASE TABLE
(8 rows)
2.8 查看搜索模式顺序
musicdb=> show SEARCH_PATH;
search_path
----------------
"$user",public
(1 row)
-- 可以看到搜索模式的顺序是先搜索user，再搜索public2.9 使用user1访问musicdb库下不同模式的同名表
musicdb=> select * from schema1.tb01;
musicdb=> content
-----------------
This is schema1
(1 row)
musicdb=> select * from schema2.tb01;
content
-----------------
This is schema2
(1 row)
musicdb=> select * from schema3.tb01;
content
-----------------
This is schema3
(1 row)
musicdb=> select * from schema4.tb01;
content
-----------------
This is schema4
(1 row)
三、学习心得
通过openGauss官网等资料了解openGauss的逻辑结构，并通过实操更形象的去理解数据库、模式、表三者之间的关系。