openGuass每日一练第16天|学习心得体会

课程学习内容

软件版本 ：openGauss 3.0.0

学习openGuass数据库中如何对表进行修改

数据库实操内容

环境准备

–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)

​ );

omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
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
omm=# 

为表添加字段

–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=# 

–为表test新增一列，列名为sex，数据类型为Boolean：

alter table test add column sex Boolean;

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

–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

omm=# 

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 ;

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

\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=# 

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;

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：

\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

omm=# 

–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';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | con
frelid | confupdtype | confdeltype | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | con
key | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+----
-------+-------------+-------------+---------------+------------+-------------+--------------+---------+--------+----
----+---------+-----------+-----------+-----------+-----------+--------+--------+--------------
(0 rows)

omm=# 

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);

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：

select * from pg_constraint where conname like ‘test_pkey’;

\d test

omm=# select * from pg_constraint  where conname like 'test_pkey';
-----------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+--
---------+-------------+-------------+---------------+------------+-------------+--------------+---------+--------+--
------+---------+-----------+-----------+-----------+-----------+--------+--------+--------------
 test_pkey |         2200 | p       | f             | f           | t            |    16389 |        0 |    16395 |  
       0 |             |             |               | t          |           0 | t            | f       | f      | {
1}    |         |           |           |           |           |        |        | 
(1 row)

  conname  | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | c
onfrelid | confupdtype | confdeltype | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | c
onkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
omm=# \d test
omm=#              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=# 

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=# \d test
 age    | integer               | default 25
Indexes:
    "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

omm=# 

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=# \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

omm=# 

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=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
omm=#  name   | character varying(50) | not null
 stuage | bigint                | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default


omm=# 

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=# \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

omm=# 

删除表

DROP TABLE mytest;

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

课程作业

创建表，为表添加字段

omm=# create table test1(
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 "test1_pkey" for table "test1"
CREATE TABLE
omm=# \d test1
            Table "public.test1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "test1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# alter table test1 add column sex Boolean;
ALTER TABLE
omm=# \d test1
omm=#             Table "public.test1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
 sex    | boolean               | 
Indexes:
    "test1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default


omm=# 

删除表中的已有字段

omm=# alter table test1 drop column sex ;
ALTER TABLE
omm=# 

删除表的已有约束、添加约束

omm=# alter table test1 drop constraint test1_pkey;
ALTER TABLE
omm=# 
omm=# \d test1
            Table "public.test1"
 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 'test1_pkey';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | con
frelid | confupdtype | confdeltype | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | con
key | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+----
-------+-------------+-------------+---------------+------------+-------------+--------------+---------+--------+----
----+---------+-----------+-----------+-----------+-----------+--------+--------+--------------
(0 rows)

omm=# 

修改表字段的默认值

omm=# alter table test1 alter column age set default 25;
ALTER TABLE
omm=# \d test1
            Table "public.test1"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 25

omm=# 

修改表字段的数据类型

omm=# alter table test1 ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# 

修改表字段的名字

omm=# ALTER TABLE test1 RENAME COLUMN age TO stuage;
ALTER TABLE
omm=# 

修改表的名字

omm=# ALTER TABLE test1 RENAME TO testok;
ALTER TABLE
omm=# \d testok
            Table "public.testok"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25

omm=# 

删除表

omm=# DROP TABLE testok;
DROP TABLE
omm=# 

课程学习体会

 通过本次的实训操作，掌握数据库的表进行修改，添加字段、修改约束条件、修改默认值等操作。