openGauss每日一练第16天 | 学习心得体会

openGuass数据库中如何对表进行修改？
1.创建表，为表添加字段

-- 连接openGuass数据库
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.
-- 清理测试数据
omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
omm=# drop table if exists test1;
NOTICE:  table "test1" does not exist, skipping
DROP TABLE
--首先创建一张测试表。
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
--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;
ALTER TABLE
--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

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

--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;
ALTER TABLE
--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
select * from pg_constraint  where conname like 'test_pkey';
omm=# select * from pg_constraint  where conname like 'test_pkey';
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-----
--------+---------------+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+---
--------+--------+--------+--------------
(0 rows)

 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | conf
deltype | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | co
nexclop | conbin | consrc | conincluding 
omm=# select * from pg_constraint  where conname like 'test_pkey';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | conf
deltype | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | co
nexclop | conbin | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-----
--------+---------------+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+---
--------+--------+--------+--------------
(0 rows)
--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);
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index "test_pkey" for table "test"
ALTER TABLE
--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 | co
nfdeltype | confmatchtype | 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)

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.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;
ALTER TABLE
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;
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

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 | 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 test1;
ALTER TABLE
omm=# \d test*
            Table "public.test1"
 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

   Index "public.test_pkey"
 Column |  Type  | Definition 
--------+--------+------------
 id     | bigint | id
primary key, btree, for table "public.test1"

8.删除表

omm=# DROP TABLE test1;
DROP TABLE
omm=# \d test*
Did not find any relation named "test*".