openGauss每日一练第6天 | 学习心得体会

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

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       | 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=# 
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=# 
--创建用户user1
omm=# CREATE USER user1 IDENTIFIED BY 'kunpeng@1234';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
--授予user1数据库系统的SYSADMIN权限
omm=# ALTER USER user1 SYSADMIN;
ALTER ROLE
--用户user1登录到数据库 musicdb1，创建表t11，并插入、查看数据
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)
--用户user1登录到数据库 musicdb2，创建表t21，并插入、查看数据
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=>

2.user1用户连接到数据库 musicdb1，并访问数据库musicdb1下的表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 t11;
musicdb1=>          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=> \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=> 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。

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=> \dt
                        List of relations
 Schema | Name | Type  | Owner |             Storage              
--------+------+-------+-------+----------------------------------
 public | t21  | table | user1 | {orientation=row,compression=no}
(1 row)

musicdb2=> 

实验结论：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