openGauss每日一练第 6天 | 学习心得体会

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：

–进入数据库omm，创建表空间、测试数据库

–执行下面的SQL语句，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
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–授予user1数据库系统的SYSADMIN权限：

omm=# ALTER USER user1 SYSADMIN;
ALTER ROLE
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–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;
         col1         
----------------------
 Hello openGauss! 11 
(1 row)

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–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));
musicdb2=> CREATE TABLE
 insert into t21 values('Hello openGauss! 22');
INSERT 0 1
musicdb2=>  select * from t21;
musicdb2=>          col1         
----------------------
 Hello openGauss! 22 
(1 row)

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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。
–使用user1用户连接到数据库musicdb1，访问数据库musicdb1下的表t11

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)

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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;
                      ^
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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：

omm=# \c musicdb2 user1
Password for user user1: 
musicdb2=> 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=> 

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