openGauss每日一练第6天

opengauss体系架构的学习。

一个用户一次只能连接一个数据库

1.环境准备.创建用户user1，分别在数据库musicdb1、数据库musicdb2创建表t11,t21

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@123';
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 ; 
musicdb1=>          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.user1用户连接到数据库musicdb1，并访问数据库musicdb1下的表t11

musicdb1-> \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 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 t21;
ERROR:  relation "t21" does not exist on gaussdb
LINE 1: select * from t21;

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。

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 t21;
         col1         
----------------------
 hello opengauss! 22 
(1 row)