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

##课程学习
1.测试准备

–首先创建一张测试表。
drop table if exists test;
create table test(
id bigint,
name varchar(50) not null,
age int default 20,
primary key(id)
);

root@modb:~#
root@modb:~# su - omm
omm@modb:~$ 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=#
omm=# drop table if exists test;
NOTICE: table “test” does not exist, skipping
DROP TABLE
omm=#
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

2.为表添加字段

–查看表test的信息
\d test

–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
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# 
omm=# 
omm=# alter table test add column sex Boolean;
ALTER TABLE
omm=#   
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

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

–或直接查看约束是否被删除
select * from pg_constraint where conname like ‘test_pkey’;

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

omm=# 
omm=# select * from pg_constraint where conname like 'test_pkey'; 
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confre
lid | confupdtype | confdeltype | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | 
confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-------
----+-------------+-------------+---------------+------------+-------------+--------------+---------+--------+--------+-
--------+-----------+-----------+-----------+-----------+--------+--------+--------------
(0 rows)

5.为表添加约束

–执行下面的SQL命令，为表test添加刚刚删除的主键约束：
alter table test add constraint test_pkey primary key(id);

–再次查看表test的信息：
select * from pg_constraint where conname like ‘test_pkey’;

\d test

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
omm=# 
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

6.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
alter table test alter column age set default 25;
\d test

omm=# alter table test alter column age set default 25;
ALTER TABLE
omm=# 
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:

7.修改表字段的数据类型

alter table test ALTER COLUMN age TYPE bigint;
\d test

omm=# alter table test ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# 
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

8.修改表字段的名字

ALTER TABLE test RENAME COLUMN age TO stuage;
\d test

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

9.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：
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 | bigint                | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

10.删除表

DROP TABLE mytest;

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