openGauss每日一练第16天 | 学习心得体会

1.创建表，为表添加字段

drop table if exists test;
create table test(
      id bigint,
      name varchar(50) not null,
      age  int default 20,
      primary key(id)
     );
--查看表test的信息
\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

--为表test新增一列，列名为sex，数据类型为Boolean：
alter table test add column sex Boolean;

--执行下面gsql命令，查看表test的信息
\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
 sex    | boolean               | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

2.删除表中的已有字段

--执行下面的SQL语句，删除刚刚添加的列sex：
alter table test drop column sex ;

--执行下面gsql命令，再次查看表test的信息
\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

3.删除表的已有约束、添加约束

alter table test drop constraint test_pkey;

--执行下面的gsql命令，再次查看表test的信息：
\d test
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

--或直接查看约束是否被删除
select * from pg_constraint  where conname like 'test_pkey';
(0 rows)

4.修改表字段的默认值

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

5.修改表字段的数据类型

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

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 | integer               | default 25

7.修改表的名字

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

8.删除表

DROP TABLE mytest;