openGauss每日一练第6天 | openGauss中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

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）

学习目标

当用户user1连接到数据库musicdb1上时，没法访问数据库musicdb2上的表。

1.测试环境准备：

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.
--进入数据库omm，创建表空间、测试数据库
omm=# drop database if exists musicdb;
NOTICE:  database "musicdb" does not exist, skipping
DROP DATABASE
omm=# drop database if exists musicdb1;
NOTICE:  database "musicdb1" does not exist, skipping
DROP DATABASE
omm=# drop database if exists musicdb2;
NOTICE:  database "musicdb2" does not exist, skipping
DROP DATABASE
omm=# drop database if exists musicdb3;
NOTICE:  database "musicdb3" does not exist, skipping
DROP DATABASE
omm=# drop tablespace if exists music_tbs;
NOTICE:  Tablespace "music_tbs" does not exist, skipping.
DROP TABLESPACE
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=# 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=# \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');
INSERT 0 1
musicdb2=> select * from t21;
         col1         
----------------------
 Hello opengauss! 22 
(1 row)

2.使用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。

musicdb2=> \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)

3.在这个连接中（使用数据库用户user1连接到数据库musicdb1），如果试图访问数据库musicdb2下的t21表会报错：

musicdb1=> select * from musicdb2.public.t21;
ERROR:  cross-database references are not implemented: "musicdb2.public.t21"
LINE 1: select * from musicdb2.public.t21;

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。
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)

课后作业

1.创建用户userA，分别在数据库musicdb1、数据库musicdb2创建表t11,t21

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;
DROP DATABASE
omm=# drop database if exists musicdb3;
NOTICE:  database "musicdb3" does not exist, skipping
DROP DATABASE
omm=# drop tablespace if exists music_tbs;
DROP TABLESPACE
omm=# create tablespace music_tbs relative location 'tablespace/test_ts1';
CREATE TABLESPACE
omm=# create database musicdb1 with tablespace = music_tbs ;
CREATE DATABASE
omm=# create database musicdb2 with tablespace = music_tbs ;
CREATE DATABASE
omm=# create user userA identified by 'kunpeng@1234';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# alter user userA sysadmin ;
ALTER ROLE
ALTER ROLEomm=# \c musicdb1 userA
Password for user usera: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb1" as user "usera".
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 userA
Password for user usera: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "usera".
musicdb2=>  create table t21(col1 char(20));
CREATE TABLE
musicdb2=> insert into t21 values('Hello openGauss! 22');
INSERT 0 1
musicdb2=>  select * from t21;
musicdb2=>          col1         
----------------------
 Hello openGauss! 22 
(1 row)

2.userA用户连接到数据库musicdb1，并访问数据库musicdb1下的表t11

musicdb2=> \c musicdb1 userA
Password for user usera: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb1" as user "usera".
musicdb1=> select * from musicdb1.public.t11;
         col1         
----------------------
 Hello openGauss! 11 
(1 row)

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)

musicdb1=> select * from musicdb2.public.t21;
ERROR:  cross-database references are not implemented: "musicdb2.public.t21"
LINE 1: select * from musicdb2.public.t21;

4.使用数据库用户userA连接到数据库musicdb2，访问数据库musicdb2下的t21表。

musicdb1=> \c musicdb2 userA
Password for user usera: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "usera".
musicdb2=> select * from musicdb2.public.t21;
         col1         
----------------------
 Hello openGauss! 22 
(1 row)