openGauss每日一练第6天 | 学习心得体会

1.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。

2.当用户user1连接到数据库musicdb1上时，没法访问数据库musicdb2上的表。
2.1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。
2.2 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：
2.3 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：
`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=# omm=#
–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
omm=# DROP DATABASE
drop tablespace IF EXISTS music_tbs;
NOTICE: Tablespace “music_tbs” does not exist, skipping.
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=# --执行下面的SQL语句，创建用户user1：
omm=#
omm=# CREATE USER user1 IDENTIFIED BY ‘kunpeng@1234’;
NOTICE: The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=#
omm=# --授予user1数据库系统的SYSADMIN权限：
omm=#
omm=# ALTER USER user1 SYSADMIN;
ALTER ROLE

omm=# --用户user1登录到数据库musicdb1，创建表t11，并插入、查看数据
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');
INSERT 0 1
musicdb2=>  select * from t21;
         col1         
----------------------
 Hello openGauss! 22 
(1 row)

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 musicdb2.public.t21;
ERROR:  cross-database references are not implemented: "musicdb2.public.t21"
LINE 1: select * from musicdb2.public.t21;
                      ^
musicdb1=> ERROR:  cross-database references are not implemented: "musicdb2.public.t21"
musicdb1-> LINE 1: select * from musicdb2.public.t21;
ERROR:  syntax error at or near "ERROR"
LINE 1: ERROR:  cross-database references are not implemented: "musi...
        ^
musicdb1=> --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)

musicdb2=>