1.创建表，为表添加字段
--首先创建一张测试表。
omm=# drop table if exists test;
omm=# create table test(id bigint,name varchar(50) not null,age int default 20, primary key(id));
2.删除表中的已有字段
--查看表test的信息
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
--为表test新增一列，列名为sex，数据类型为Boolean：
omm=# alter table test add column sex Boolean;
--执行下面gsql命令，查看表test的信息
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
--执行下面的SQL语句，删除刚刚添加的列sex：
omm=# alter table test drop column sex;
--执行下面gsql命令，再次查看表test的信息
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
3.删除表的已有约束、添加约束
删除表的已有约束
--表test上有一个名叫test_pkey的PRIMARY KEY约束。执行下面的SQL语句，删除这个约束：
omm=# alter table test drop constraint test_pkey;
--执行下面的gsql命令，再次查看表test的信息：
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
--或直接查看约束是否被删除
omm=# select * from pg_constraint where conname like 'test_pkey';
conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding
---------+--------------+---------+---------------+-------------+--------------+---
-------+----------+----------+-----------+-------------+-------------+-------------
--+------------+-------------+--------------+---------+--------+--------+---------+
-----------+-----------+-----------+-----------+--------+--------+--------------
(0 rows)
conname | connamespace | contype | condeferrable | condeferred | convalidated | co
nrelid | contypid | conindid | confrelid | confupdtype | confdeltype | confmatchtyp
e | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey |
omm=#--执行下面的SQL命令，为表test添加刚刚删除的主键约束：
omm=# alter table test add constraint test_pkey primary key(id);
--再次查看表test的信息：
omm=# select * from pg_constraint where conname like 'test_pkey';
conname | connamespace | contype | condeferrable | condeferred | convalidated |
conrelid | contypid | conindid | confrelid | confupdtype | confdeltype | confmatcht
ype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey
| conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding
-----------+--------------+---------+---------------+-------------+--------------+-
---------+----------+----------+-----------+-------------+-------------+-----------
----+------------+-------------+--------------+---------+--------+--------+--------
-+-----------+-----------+-----------+-----------+--------+--------+--------------
test_pkey | 2200 | p | f | f | t |
16389 | 0 | 16395 | 0 | | |
| t | 0 | t | f | f | {1} |
| | | | | | |
(1 row)
\d test
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
4.修改表字段的默认值
--执行下面的SQL语句，将age的默认值变更为25
omm=# alter table test alter column age set default 25;
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
5.修改表字段的数据类型
omm=# alter table test alter column age type bigint;
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
6.修改表字段的名字
omm=# alter table test rename column age to stuage;
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
stuage | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
7.修改表的名字
--修改表的名字。执行下面的SQL语句，将表test的名字变更为mytest：
omm=# alter table test rename to mytest;
omm=# \d mytest
Table "public.mytest"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
stuage | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
8.删除表
omm=# drop table mytest;
