学习目标

学习openGuass数据库中如何对表进行修改

课程作业

1.创建表，为表添加字段

newdb1=# create table test(id bigint,name varchar(50) not null,age  int default 20,primary key(id));
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE


newdb1=# \d test
             Table "testsm.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 newtbs1

newdb1=# alter table test add column sex Boolean;
ALTER TABLE
newdb1=# \d test
             Table "testsm.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 newtbs1

2.删除表中的已有字段

newdb1=# alter table test drop column sex ;
ALTER TABLE
newdb1=# \d test
             Table "testsm.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 newtbs1

3.删除表的已有约束、添加约束

--删除主键约束
newdb1=# \d test
             Table "testsm.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 newtbs1

newdb1=# alter table test drop constraint test_pkey;
ALTER TABLE
newdb1=# \d test
             Table "testsm.test"
 Column |         Type          | Modifiers
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20

--添加主键约束
newdb1=# 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
newdb1=# \d test
             Table "testsm.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 newtbs1

newdb1=#

4.修改表字段的默认值

newdb1=# \d test
             Table "testsm.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 newtbs1

newdb1=# alter table test alter column age set default 25;
ALTER TABLE
newdb1=# \d test
             Table "testsm.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 newtbs1

5.修改表字段的数据类型

newdb1=# \d test
             Table "testsm.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 newtbs1

newdb1=# alter table test ALTER COLUMN age TYPE bigint;
ALTER TABLE
newdb1=# \d test
             Table "testsm.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 newtbs1

6.修改表字段的名字

newdb1=# ALTER TABLE test RENAME COLUMN age TO stuage;
ALTER TABLE
newdb1=# \d test
             Table "testsm.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 newtbs1

7.修改表的名字

newdb1=# ALTER TABLE test RENAME TO mytest;
ALTER TABLE
newdb1=# \d test
Did not find any relation named "test".
newdb1=# \d mytest
            Table "testsm.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 newtbs1

8.删除表

newdb1=# DROP TABLE mytest;
DROP TABLE
newdb1=# \d mytest
Did not find any relation named "mytest".