openGauss每日一练第11天 | openGauss体系结构

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。

# 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;

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

CREATE TABLESPACE
omm=# 
omm=# CREATE DATABASE musicdb WITH TABLESPACE = enmtbs;

CREATE DATABASE

# 2.查看数据库集簇中有哪些数据库

omm=# SELECT datname FROM pg_database;
  datname  
-----------
 template1
 omm
 musicdb
 template0
 postgres
(5 rows)

omm=# 
\l
omm=#                          List of databas
es
   Name    | 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/omm
 template1 | omm   | UTF8     | C       
| C     | =c/omm           +
           |       |          |         
|       | omm=CTc/omm
(5 rows)

# 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：

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

–根据表空间对象的OID，来查看表空间的名字：

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

–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：

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

# 4.查看数据库下有哪些模式

omm=# omm=# 

omm=# \dn+
                                        
 List of schemas
      Name       | Owner | Access privil
eges |           Description            
| WithBlockChain 
-----------------+-------+--------------
-----+----------------------------------
+----------------
 blockchain      | omm   |              
     | blockchain schema                
| f
 cstore          | omm   |              
     | reserved schema for DELTA tables 
| f    +| db4ai schema                     
| f
                 |       | =U/omm       
     |                                  
| 

 db4ai           | omm   | omm=UC/omm   
--More-- dbe_perf        | omm   |              
     | dbe_perf schema                  
| f
 dbe_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               
| f
 public          | omm   | omm=UC/omm   
    +| standard public schema           
| f
                 |       | =U/omm       
     |                                  
| 
 snapshot        | omm   |              
     | snapshot schema                  
| f
 sqladvisor      | omm   | omm=UC/omm   
    +| sqladvisor schema                
| f
                 |       | =U/omm       
     |                                  
| 
(10 rows)

# 5.查询当前连接的数据库omm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_type
from information_schema.tables
where 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(# omm(#           from information_stablest
 ('pg_catalog', 'information_schema','dbe_perf')
omm(#        )
omm-# omm-# 
 select * from my_tables;
 table_catalog |  table_schema   | table
_name | table_type 
---------------+-----------------+------
------+------------
 omm           | db4ai           | snaps
hot   | BASE TABLE
 omm           | dbe_pldeveloper | gs_er
rors  | BASE TABLE
 omm           | dbe_pldeveloper | gs_so
urce  | BASE TABLE
(3 rows)

# 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=# 
omm=# ALTER DATABASE musicdb  SET TABLESPACE app_ts;
ALTER DATABASE
�mm=# --查看表空间是否更改完成
omm=# omm-# select spcname 
from pg_tablespace 
omm-# where oid=( select dattablespace
omm(#            from pg_database
omm(#            where datname='musicdb' );
 spcname 
---------
 app_ts
(1 row)

# 7.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=# 
omm=# \l
                         List of databas
es
   Name    | 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/omm
(5 rows)

           |       |          |         
|       | omm=CTc/omm
 template1 | omm   | UTF8     | C       
| C     | =c/omm           +

# 8.重新命名数据库

omm=# ALTER DATABASE musicdb RENAME TO  musicdb1;
ALTER DATABASE
omm=# \l
                         List of databas
es
   Name    | 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/omm


 template1 | 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=#