第 4 天课程打卡，本节课程目标为“学习 openGauss 体系结构，使用多个用户访问同一个数据库”。

学习内容

跟着课程学习的内容完成了操作验证，正如标题，我们本课需要重点掌握用户访问数据库的方法，也就是 \c 元命令的使用，这里贴出它的参数：

\c[onnect] [DBNAME|- USER|- HOST|- PORT|-]

使用 \c 加数据库名称，再加用户名称，即可使用指定用户访问到指定的数据。如：

\c musicdb2 user1

以下是作业实操记录。

课后作业

1. 创建用户 user1、user2、user3，授予 user1、user2、user3 数据库系统的 SYSADMIN 权限

omm=# CREATE TABLESPACE music_tbs RELATIVE LOCATION 'tablespace/test_ts1';
CREATE TABLESPACE
omm=# CREATE DATABASE musicdb2  WITH TABLESPACE = music_tbs;
CREATE DATABASE

omm=# CREATE USER user1 IDENTIFIED BY 'Tank@Modb';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# CREATE USER user2 IDENTIFIED BY 'Tank@Modb';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# CREATE USER user3 IDENTIFIED BY 'Tank@Modb';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# 

omm=# ALTER USER user1 SYSADMIN;
ALTER ROLE
omm=# ALTER USER user2 SYSADMIN;
ALTER ROLE
omm=# ALTER USER user3 SYSADMIN;
ALTER ROLE
omm=# \du
                                                              List of roles
 Role name |                                                    Attributes                                                    | Me
mber of 
-----------+------------------------------------------------------------------------------------------------------------------+---
--------
 gaussdb   | Sysadmin                                                                                                         | {}
 user2     | Sysadmin                                                                                                         | {}
 user3     | Sysadmin                                                                                                         | {}

 omm       | Sysadmin, Create role, Create DB, Replication, Administer audit, Monitoradmin, Operatoradmin, Policyadmin, UseFT | {}
 user1     | Sysadmin                                                                                                         | {}

2. 分别使用 user1、user2、user3 访问数据库musicdb2，创建各自的表，并插入数据。表名和数据如下：

表名分别为： products1、 products2、 products3

omm=# \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 products1(product_id int,product_name char(20),category char(30));
CREATE TABLE

insert into products1 values
(1502,'olympus camera','electrncs'),
(1601,'lamaze','toys'),
(1700,'wait interface','Books'),
(1666,'harry potter','toys');

musicdb2=> select * from products1;
 product_id |     product_name     |            category          
------------+----------------------+--------------------------------
       1502 | olympus camera       | electrncs                   
       1601 | lamaze               | toys                        
       1700 | wait interface       | Books                       
       1666 | harry potter         | toys                        
(4 rows)


musicdb2=> \c musicdb2 user2
Password for user user2: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "user2".
musicdb2=> create table products2(product_id int,product_name char(20),category char(30));
CREATE TABLE

insert into products2 values
(1502,'olympus camera','electrncs'),
(1601,'lamaze','toys'),
(1700,'wait interface','Books'),
(1666,'harry potter','toys');

musicdb2=> select * from products2;
 product_id |     product_name     |            category          
------------+----------------------+--------------------------------
       1502 | olympus camera       | electrncs                   
       1601 | lamaze               | toys                        
       1700 | wait interface       | Books                       
       1666 | harry potter         | toys                        
(4 rows)

musicdb2=> \c musicdb2 user3
Password for user user3: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "user3".
musicdb2=> 
  
musicdb2=> create table products3(product_id int,product_name char(20),category char(30));
CREATE TABLE

insert into products3 values
(1502,'olympus camera','electrncs'),
(1601,'lamaze','toys'),
(1700,'wait interface','Books'),
(1666,'harry potter','toys');

musicdb2=> select * from products3;
 product_id |     product_name     |            category          
------------+----------------------+--------------------------------
       1502 | olympus camera       | electrncs                   
       1601 | lamaze               | toys                        
       1700 | wait interface       | Books                       
       1666 | harry potter         | toys                        
(4 rows)

3. 使用 user1、user2、user3 用户中的任何一个，查看当前数据库musicdb2有哪些表

musicdb2=> \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=> \dt
                           List of relations
 Schema |   Name    | Type  | Owner |             Storage            
--------+-----------+-------+-------+----------------------------------
 public | products1 | table | user1 | {orientation=row,compression=no}
 public | products2 | table | user2 | {orientation=row,compression=no}
 public | products3 | table | user3 | {orientation=row,compression=no}
(3 rows)

musicdb2=> \c musicdb2 user2
Password for user user2: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "user2".
musicdb2=> \dt
                           List of relations
 Schema |   Name    | Type  | Owner |             Storage            
--------+-----------+-------+-------+----------------------------------
 public | products1 | table | user1 | {orientation=row,compression=no}
 public | products2 | table | user2 | {orientation=row,compression=no}
 public | products3 | table | user3 | {orientation=row,compression=no}
(3 rows)


musicdb2=> \c musicdb2 user3
Password for user user3: 
Non-SSL connection (SSL connection is recommended when requiring high-security)
You are now connected to database "musicdb2" as user "user3".
musicdb2=> \dt
                           List of relations
 Schema |   Name    | Type  | Owner |             Storage            
--------+-----------+-------+-------+----------------------------------
 public | products1 | table | user1 | {orientation=row,compression=no}
 public | products2 | table | user2 | {orientation=row,compression=no}
 public | products3 | table | user3 | {orientation=row,compression=no}
(3 rows)

总结

在运维过程中，灵活使用 \c 元命令可快速通过指定用户访问指定数据库。

-- 方法 1:
gsql -d musicdb2 -U user1

-- 方法 2：
\c musicdb2 user1

历史打卡记录：

openGauss 每日一练第 1 天｜openGauss 数据库状态查看

openGauss 每日一练第 2 天｜学习 openGauss 客户端工具 gsql 的使用

openGauss 每日一练第 3 天｜openGauss 中一个数据库集簇对应多个数据库