openGauss每日一练第 11 天| 学习心得体会

学习心得

本节课复习了常见数据库，创建数据库，查看数据库信息，修改默认表空间，并学习了修改数据库名称（好方便，但是不知道真的会有场景需要修改DB名称么），顺便自己还复习了一下怎么创建schema，在schema下建表，温故也是一种乐趣

课后作业

1.创建表空间enmtbs和数据库musicdb

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

omm=# \l
                         List of databases
   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)

omm=# select datname from pg_database;
  datname  
-----------
 template1
 omm
 musicdb
 template0
 postgres
(5 rows)

3.查看数据库默认的表空间信息

omm=# select datname,dattablespace from pg_database where datname='musicdb';

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

4.查看数据库下有哪些模式

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

omm=# SELECT catalog_name, schema_name, schema_owner FROM information_schema.schemata;
 catalog_name |    schema_name     | schema_owner 
--------------+--------------------+--------------
 omm          | pg_toast           | omm
 omm          | cstore             | omm
 omm          | pkg_service        | omm
 omm          | dbe_perf           | omm
 omm          | snapshot           | omm
 omm          | blockchain         | omm
 omm          | pg_catalog         | omm
 omm          | public             | omm
 omm          | sqladvisor         | omm
 omm          | dbe_pldebugger     | omm
 omm          | dbe_pldeveloper    | omm
 omm          | information_schema | omm
 omm          | db4ai              | omm
(13 rows)

5.查询当前连接的数据库下有哪些表：

omm-# 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;

 table_catalog |  table_schema   | table_name | table_type 
---------------+-----------------+------------+------------
 omm           | db4ai           | snapshot   | BASE TABLE
 omm           | dbe_pldeveloper | gs_errors  | BASE TABLE
 omm           | dbe_pldeveloper | gs_source  | BASE TABLE
 omm           | xxs1            | xxs        | BASE TABLE
 omm           | public          | xxs        | BASE TABLE
(5 rows)

6.更改数据库默认的表空间

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
           from pg_database
           where datname='musicdb' );
 spcname 
---------
 app_ts
(1 row)

omm=# 

7.重新命名数据库

omm=# ALTER DATABASE musicdb RENAME TO  musicdb1;
ALTER DATABASE
omm=# 
omm=# \l
                         List of databases
   Name    | Owner | Encoding | Collate | Ctype | Access privileges 
-----------+-------+----------+---------+-------+-------------------
 musicdb1  | 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=#            |       |          |         |       | omm=CTc/omm
(5 rows)

8.修改数据库的默认用户

omm=# ALTER DATABASE musicdb1 OWNER to user1;
ALTER DATABASE

9.删除数据库

omm=# drop database musicdb1;
DROP DATABASE