openGauss每日一练第16天

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

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=# drop table if exists t1;
NOTICE:  table "t1" does not exist, skipping
DROP TABLE
omm=# create table t1(
      id bigint,
      name varchar(50) not null,
      age  int default 20,
      primary key(id)
      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t1_pkey" for table "t1"
CREATE TABLE
 

2.删除表中的已有字段

omm=# alter table t1 add column sex Boolean;
ALTER TABLE
omm=# \d t1
              Table "public.t1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
 sex    | boolean               | 
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=#alter table t1 drop column sex ;
ALTER TABLE
omm=# \d t1
              Table "public.t1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

3.删除表的已有约束、添加约束

omm=# alter table t1 drop constraint t1_pkey;
ALTER TABLE
omm=# alter table t1 add constraint t1_pkey primary key(id);
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index "t1_pkey" for table "t1"
ALTER TABLE

4.修改表字段的默认值

omm=# alter table t1 alter column age set default 25;
ALTER TABLE
omm-# \d t1
              Table "public.t1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 25
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

5.修改表字段的数据类型

omm=# alter table t1 ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# \d t1
              Table "public.t1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | bigint                | default 25
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

6.修改表字段的名字

omm=# ALTER TABLE t1 RENAME COLUMN age TO stuage;
ALTER TABLE
omm=# \d t1
              Table "public.t1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

7.修改表的名字

omm=# ALTER TABLE t1 RENAME TO myt1;
ALTER TABLE
omm=# \d myt1
             Table "public.myt1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

8.删除表

omm=# DROP TABLE myt1;
DROP TABLE
omm=# \d myt1
Did not find any relation named "myt1".
omm=#