openGauss每日一练第16天-表管理4

原创陈军 2022-12-09
238
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)
     );
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
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
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';
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
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
7.修改表字段的数据类型
alter table test ALTER COLUMN age TYPE bigint;
\d test
8.修改表字段的名字
ALTER TABLE test RENAME COLUMN age TO stuage;
\d test
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
10.删除表
DROP TABLE mytest;
课程作业
1.创建表，为表添加字段
```sql
omm=# create table d(id int ,name varchar(20) not null ,age int default 20,primary key(id));
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "d_pkey" for table "d"
CREATE TABLE
omm=# \d d;
omm=#               Table "public.d"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | integer               | not null
 name   | character varying(20) | not null
 age    | integer               | default 20
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default


omm=# alter table d add column sex int;
ALTER TABLE
omm=# \d d;
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=#               Table "public.d"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | integer               | not null
 name   | character varying(20) | not null
 age    | integer               | default 20
 sex    | integer               | 
```
2.删除表中的已有字段
```sql

omm=# alter table d drop column sex;
ALTER TABLE
omm=# \d d;
              Table "public.d"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
omm=#  id     | integer               | not null
 name   | character varying(20) | not null
 age    | integer               | default 20
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default


```
3.删除表的已有约束、添加约束
```sql

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

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

omm=# alter table d add constraint d_pkey primary key(id); 
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index "d_pkey" for table "d"
ALTER TABLE
omm=# select * from pg_constraint where conname like 'd_pkey';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid |
 conindid | confrelid | confupdtype | confdeltype | confmatchtype | conislocal | coninhcount | connoin
herit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin |
 consrc | conincluding 
(1 row)

---------+--------------+---------+---------------+-------------+--------------+----------+----------+
----------+-----------+-------------+-------------+---------------+------------+-------------+--------
------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+--------+
--------+--------------
 d_pkey  |         2200 | p       | f             | f           | t            |    16389 |        0 |
    16395 |         0 |             |             |               | t          |           0 | t      
      | f       | f      | {1}    |         |           |           |           |           |        |
        | 
omm=# 
omm=# 
omm=# \d d;
              Table "public.d"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | integer               | not null
 name   | character varying(20) | not null
 age    | integer               | default 20
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

```
4.修改表字段的默认值
```sql

omm=# alter table d alter column age set  default 25;
ALTER TABLE
omm=# \d d;
              Table "public.d"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | integer               | not null
 name   | character varying(20) | not null
 age    | integer               | default 25
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default


```
5.修改表字段的数据类型
```sql

omm=# alter table d alter column name type  char(30)
omm-# ;
ALTER TABLE
omm=# \d d;
          Table "public.d"
 Column |     Type      | Modifiers  
--------+---------------+------------
 id     | integer       | not null
 name   | character(30) | not null
 age    | integer       | default 25
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

```
6.修改表字段的名字
```sql

omm=# alter table d rename column age to stuage;
ALTER TABLE
omm=# \d d;
          Table "public.d"
 Column |     Type      | Modifiers  
--------+---------------+------------
 id     | integer       | not null
 name   | character(30) | not null
 stuage | integer       | default 25
Indexes:
    "d_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default


```
7.修改表的名字
```sql
omm=# alter table d rename to d1;
ALTER TABLE



```
8.删除表
```sql

omm=# drop table d1;
DROP TABLE
```
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