一、学习目标
学习openGauss体系结构，通过实验，了解用户一次只能连接到一个数据库，没法访问其他数据库的对象。（注：本实验没有使用dblink插件）
二、课程学习
当用户user1连接到数据库musicdb1上时，没法访问数据库musicdb2上的表。
三、课程作业
1. 创建用户user1，分别在数据库musicdb1、数据库musicdb2创建表t11,t21
--登陆连接数据库，创建表空间和数据库musicdb1、musicdb2，用户user1
su - omm
gsql -r
--进入数据库omm，创建表空间、测试数据库
drop DATABASE IF EXISTS musicdb;
drop DATABASE IF EXISTS musicdb1;
drop DATABASE IF EXISTS musicdb2;
drop DATABASE IF EXISTS musicdb3;
drop tablespace IF EXISTS music_tbs;
CREATE TABLESPACE music_tbs RELATIVE LOCATION 'tablespace/test_ts1';
CREATE DATABASE musicdb WITH TABLESPACE = music_tbs;
CREATE DATABASE musicdb1 WITH TABLESPACE = music_tbs;
CREATE DATABASE musicdb2 WITH TABLESPACE = music_tbs;
--执行下面的SQL语句，删除创建用户user1：
DROP USER USER1 CASCADE;
CREATE USER user1 IDENTIFIED BY 'kunpeng@1234';
--授予user1数据库系统的SYSADMIN权限：
ALTER USER user1 SYSADMIN;
--查看数据库用户和角色
\du
--用户user1登录到数据库musicdb1，创建表t11，并插入、查看数据
\c musicdb1 user1
create table t11(col1 char(20));
insert into t11 values('Hello openGauss! 11');
select * from t11;
--用户user1登录到数据库musicdb2，创建表t21，并插入、查看数据
\c musicdb2 user1
create table t21(col1 char(20));
insert into t21 values('Hello openGauss! 22');
select * from t21;
实训环境示例：
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=# drop DATABASE IF EXISTS musicdb;
DROP DATABASE
omm=# drop DATABASE IF EXISTS musicdb1;
DROP DATABASE
omm=# drop DATABASE IF EXISTS musicdb2;
omm=# drop DATABASE IF EXISTS musicdb3;
NOTICE: database "musicdb3" does not exist, skipping
DROP DATABASE
DROP DATABASE
omm=# drop tablespace IF EXISTS music_tbs;
DROP TABLESPACE
omm=#
omm=# CREATE TABLESPACE music_tbs RELATIVE LOCATION 'tablespace/test_ts1';
CREATE TABLESPACE
omm=# CREATE DATABASE musicdb WITH TABLESPACE = music_tbs;
CREATE DATABASE
omm=# CREATE DATABASE musicdb1 WITH TABLESPACE = music_tbs;
CREATE DATABASE
omm=# CREATE DATABASE musicdb2 WITH TABLESPACE = music_tbs;
CREATE DATABASE
omm=#
omm=# \db
List of tablespaces
Name | Owner | Location
------------+-------+---------------------
music_tbs | omm | tablespace/test_ts1
pg_default | omm |
pg_global | omm |
(3 rows)
omm=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+-------+----------+---------+-------+-------------------
musicdb | omm | UTF8 | C | C |
musicdb1 | omm | UTF8 | C | C |
musicdb2 | 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
(7 rows)
omm=#
omm=# DROP USER USER1 CASCADE;
DROP ROLE
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
omm=# \du
List of roles
Role name | Attributes | Member of
-----------+------------------------------------------------------------------------------------------------------------------+-----------
gaussdb | Sysadmin | {
}
omm | Sysadmin, Create role, Create DB, Replication, Administer audit, Monitoradmin, Operatoradmin, Policyadmin, UseFT | {
}
user1 | Sysadmin | {
}
omm=#
omm=# \c musicdb1 user1
Password for user user1:
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb1" as user "user1".
musicdb1=> create table t11(col1 char(20));
CREATE TABLE
musicdb1=> insert into t11 values('Hello openGauss! 11');
INSERT 0 1
musicdb1=> select * from t11;
col1
----------------------
Hello openGauss! 11
(1 row)
musicdb1=> \c musicdb2 user1
Password for user user1:
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "user1".
musicdb2=> create table t21(col1 char(20));
CREATE TABLE
musicdb2=> insert into t21 values('Hello openGauss! 22');
musicdb2=> select * from t21;INSERT 0 1
col1
----------------------
Hello openGauss! 22
(1 row)
musicdb2=>
2. user1用户连接到数据库musicdb1，并访问数据库musicdb1下的表t11
--可以使用DatabaseName.SchemaName.TableName来标识openGauss中的一个表。
使用user1用户连接到数据库musicdb1，访问数据库musicdb1下的表t11
\c musicdb1 user1
select * from musicdb1.public.t11;
omm=# \c musicdb1 user1
Password for user user1:
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb1" as user "user1".
musicdb1=> select * from musicdb1.public.t11;
col1
----------------------
Hello openGauss! 11
(1 row)
musicdb1=>
3. 在这个连接中（使用数据库用户user1连接到数据库musicdb1）访问数据库musicdb2下的t21表(会报错)
select * from musicdb2.public.t21;
musicdb1=> select * from musicdb2.public.t21;
ERROR: cross-database references are not implemented: "musicdb2.public.t21"
LINE 1: select * from musicdb2.public.t21;
^
musicdb1=>
4. 使用数据库用户user1连接到数据库musicdb2，访问数据库musicdb2下的t21表。
--可以正常访问，数据库中的表是存在的。但不能跨库访问。
\c musicdb2 user1
select * from musicdb2.public.t21;
musicdb1=> \c musicdb2 user1
Password for user user1:
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "user1".
musicdb2=> select * from musicdb2.public.t21;
col1
----------------------
Hello openGauss! 22
(1 row)
musicdb2=>