一、学习目标

数据库是数据库对象的容器，在数据库中，可以创建模式、表、索引等数据库对象。openGauss数据库管理包括：创建数据库、删除数据库、重新命名数据库、查看数据库的信息。
创建一个新的数据库。缺省情况下，新数据库将通过复制标准系统数据库template0来创建，且仅支持使用template0来创建。

二、课程作业

1.创建表空间enmtbs和数据库musicdb

su - omm
gsql -r
CREATE TABLESPACE enmtbs RELATIVE LOCATION 'tablespace/enmtbs1';
CREATE DATABASE musicdb WITH TABLESPACE = enmtbs;

实训环境示例：

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=# CREATE TABLESPACE enmtbs RELATIVE LOCATION 'tablespace/enmtbs1';
CREATE TABLESPACE
omm=# CREATE DATABASE musicdb WITH TABLESPACE = enmtbs;
CREATE DATABASE
omm=# 

2.查看数据库集簇中有哪些数据库

SELECT datname FROM pg_database;
oid相当于数据库中一个唯一标识符
SELECT oid,datname FROM pg_database;
或
\l

omm=# SELECT datname FROM pg_database;datname  
-----------template1ommmusicdbtemplate0postgres
(5 rows)omm=# SELECT oid,datname FROM pg_database;oid  |  datname  
-------+-----------1 | template116384 | omm16390 | musicdb14555 | template014560 | postgres
(5 rows)omm=# \lList of databasesName    | Owner | Encoding | Collate | Ctype | Access privileges 
-----------+-------+----------+---------+-------+-------------------musicdb   | omm   | UTF8     | C       | C     | omm       | omm   | UTF8     | C       | C     | postgres  | omm   | UTF8     | C       | C     | template0 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/ommtemplate1 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/omm
(5 rows)omm=# 

3.查看数据库默认的表空间信息
–首先执行下面的语句，查看musicdb数据库默认表空间的对象OID：
select datname,dattablespace from pg_database where datname=‘musicdb’;

omm=# select datname,dattablespace from pg_database where datname='musicdb';datname | dattablespace 
---------+---------------musicdb |         16389
(1 row)omm=# 

–根据表空间对象的OID，来查看表空间的名字:
select oid,spcname from pg_tablespace where oid=16389;

omm=# select oid,spcname from pg_tablespace where oid=16389;oid  | spcname 
-------+---------16389 | enmtbs
(1 row)omm=# 

–可以将上面的两条语句合并成一条语句，来查询数据库musicdb默认表空间的名字：
select spcname from pg_tablespace where oid=( select dattablespace
from pg_database where datname=‘musicdb’ );

omm=# select spcname from pg_tablespace where oid=( select dattablespace
omm(# from pg_database where datname='musicdb' );spcname 
---------enmtbs
(1 row)omm=# 

4.查看数据库下有哪些模式

\dn+--或
SELECT catalog_name, schema_name, schema_owner FROM information_schema.schemata;

omm=# \dn+List of schemasName       | Owner | Access privileges |           Description            | WithBloc
kChain 
-----------------+-------+-------------------+----------------------------------+---------
-------blockchain      | omm   |                   | blockchain schema                | fcstore          | omm   |                   | reserved schema for DELTA tables | fdb4ai           | omm   | omm=UC/omm       +| db4ai schema                     | f|       | =U/omm            |                                  | dbe_perf        | omm   |                   | dbe_perf schema                  | fdbe_pldebugger  | omm   | omm=UC/omm       +| dbe_pldebugger schema            | f|       | =U/omm            |                                  | dbe_pldeveloper | omm   | omm=UC/omm       +| dbe_pldeveloper schema           | f|       | =U/omm            |                                  | pkg_service     | omm   |                   | pkg_service schema               | fpublic          | omm   | omm=UC/omm       +| standard public schema           | f|       | =U/omm            |                                  | snapshot        | omm   |                   | snapshot schema                  | fsqladvisor      | omm   | omm=UC/omm       +| sqladvisor schema                | f|       | =U/omm            |                                  | 
(10 rows)
omm=# 
omm=# SELECT catalog_name, schema_name, schema_owner FROM information_schema.schemata;catalog_name |    schema_name     | schema_owner 
--------------+--------------------+--------------omm          | pg_toast           | ommomm          | cstore             | ommomm          | pkg_service        | ommomm          | dbe_perf           | ommomm          | snapshot           | ommomm          | blockchain         | ommomm          | pg_catalog         | ommomm          | public             | ommomm          | sqladvisor         | ommomm          | dbe_pldebugger     | ommomm          | dbe_pldeveloper    | ommomm          | information_schema | ommomm          | db4ai              | omm
(13 rows)omm=# 

5.查询当前连接的数据库下有哪些表：

with my_tables(table_catalog, table_schema, table_name, table_type) as(   select table_catalog, table_schema, table_name, table_typefrom information_schema.tableswhere table_schema not in ('pg_catalog', 'information_schema','dbe_perf'))select * from my_tables;

omm=# with my_tables(table_catalog, table_schema, table_name, table_type) as
omm-#       (   select table_catalog, table_schema, table_name, table_type
omm(#           from information_schema.tables
omm(#          where table_schema not in ('pg_catalog', 'information_schema','dbe_perf')
omm(# omm-#        )
omm-# select * from my_tables;table_catalog |  table_schema   | table_name | table_type 
---------------+-----------------+------------+------------omm           | db4ai           | snapshot   | BASE TABLEomm           | dbe_pldeveloper | gs_errors  | BASE TABLEomm           | dbe_pldeveloper | gs_source  | BASE TABLE
(3 rows)omm=# 

6.更改数据库默认的表空间

CREATE TABLESPACE app_ts  RELATIVE LOCATION 'tablespace/app_ts1';ALTER DATABASE musicdb  SET TABLESPACE app_ts;
--查看表空间是否更改完成
select spcname from pg_tablespace where oid=( select dattablespace
from pg_database where datname='musicdb' );

omm=# CREATE TABLESPACE app_ts  RELATIVE LOCATION 'tablespace/app_ts1';
CREATE TABLESPACE
omm=# ALTER DATABASE musicdb  SET TABLESPACE app_ts;
ALTER DATABASE
omm=# select spcname from pg_tablespace where oid=( select dattablespace
omm(# from pg_database where datname='musicdb' );spcname 
---------app_ts
(1 row)omm=# 

7.重新命名数据库

ALTER DATABASE musicdb RENAME TO  musicdb1;
\l

omm=# ALTER DATABASE musicdb RENAME TO  musicdb1;
ALTER DATABASE
omm=# \lList of databasesName    | Owner | Encoding | Collate | Ctype | Access privileges 
-----------+-------+----------+---------+-------+-------------------musicdb1  | user1 | UTF8     | C       | C     | omm       | omm   | UTF8     | C       | C     | postgres  | omm   | UTF8     | C       | C     | template0 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/ommtemplate1 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/omm
(5 rows)omm=# 

8.修改数据库的默认用户

CREATE USER user1  IDENTIFIED BY 'user1@ustb2020';
ALTER USER user1  SYSADMIN;
ALTER DATABASE musicdb OWNER to user1;\l

omm=# CREATE USER user1  IDENTIFIED BY 'user1@ustb2020';
NOTICE:  The encrypted password contains MD5 ciphertext, which is not secure.
CREATE ROLE
omm=# ALTER USER user1  SYSADMIN;
ALTER ROLE
omm=# ALTER DATABASE musicdb OWNER to user1;
ALTER DATABASE
omm=# \lList of databasesName    | Owner | Encoding | Collate | Ctype | Access privileges 
-----------+-------+----------+---------+-------+-------------------musicdb   | user1 | UTF8     | C       | C     | omm       | omm   | UTF8     | C       | C     | postgres  | omm   | UTF8     | C       | C     | template0 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/ommtemplate1 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/omm
(5 rows)omm=# 

9.删除数据库

omm=# DROP DATABASE musicdb1;
DROP DATABASE
omm=# \lList of databasesName    | Owner | Encoding | Collate | Ctype | Access privileges 
-----------+-------+----------+---------+-------+-------------------omm       | omm   | UTF8     | C       | C     | template1 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/omm
(4 rows)postgres  | omm   | UTF8     | C       | C     | template0 | omm   | UTF8     | C       | C     | =c/omm           +|       |          |         |       | omm=CTc/omm
omm=#