openGauss每日一练第16天 | 学习心得体会

学习目标

学习openGuass数据库中如何对表进行修改

课程作业

1.创建表，为表添加字段

\d test 查看表test的信息。为表test新增一列，列名为sex，数据类型为Boolean：

omm=# create table test(
      id bigint,
     name varchar(50) not null,
      age  int default 20, primary key(id)
     );     
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE

omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# alter table test add column sex Boolean;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
 sex    | boolean               | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# 

2.删除表中的已有字段

删除刚刚添加的列sex

omm=# alter table test drop column sex ;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# 

3.删除表的已有约束、添加约束

删除表test上有一个名叫test_pkey的PRIMARY KEY约束。

omm=# alter table test drop constraint test_pkey;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20

或者：
omm=# \x
Expanded display is on.
omm=# select * from pg_constraint  where conname like 'test_pkey';
(No rows)
omm=# 

4.修改表字段的默认值

omm=# select * from pg_constraint  where conname like 'test_pkey';
(No rows)
omm=# alter table test alter column age set default 25;
ALTER TABLE
omm=# \d test
omm=#              Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 25

5.修改表字段的数据类型

omm=# alter table test ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | bigint                | default 25

omm=# 

6.修改表字段的名字

omm=# ALTER TABLE test RENAME COLUMN age TO stuage;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25

omm=# 

7.修改表的名字

omm=# ALTER TABLE test RENAME TO mytest;
ALTER TABLE
omm=# \d mytest
            Table "public.mytest"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25

omm=# 

8.删除表

omm=# DROP TABLE mytest;
DROP TABLE
omm=#