目标

如何修改表 alter table

作业

1.创建表，为表添加字段

root@modb:~# su - omm
omm@modb:~$ gsql -r

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

2.删除表中的已有字段

omm=# alter table test drop column sex ;
ALTER TABLE

3.删除表的已有约束、添加约束

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

4.修改表字段的默认值

omm=# alter table test alter column age set default 25;
ALTER TABLE
omm=# \d
                        List of relations
 Schema | Name | Type  | Owner |             Storage              
--------+------+-------+-------+----------------------------------
 public | test | table | omm   | {orientation=row,compression=no}
(1 row)
omm=# \d test
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=#              Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 25
Indexes:

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
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 

6.修改表字段的名字

omm=# ALTER TABLE mytest RENAME COLUMN age TO stuage;
ALTER TABLE

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
 age    | bigint                | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

8.删除表

omm=# drop table mytest;
DROP TABLE