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首页 / openGauss每日一练第16天 |逻辑结构：表管理4

openGauss每日一练第16天 |逻辑结构：表管理4

原创 李先生 2022-12-10
280

openGauss每日一练第16天 |逻辑结构：表管理4

openGauss逻辑结构：表管理4

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。
omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
omm=# DROP TABLE
create table test(
omm(#       id bigint,
omm(#       name varchar(50) not null,
omm(#       age  int default 20,
omm(#      );
omm(#       primary key(id)
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=#

2.为表添加字段

--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

omm=# 

--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
omm=# 

--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
omm=#

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

--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

omm=#
  1. 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;
ALTER TABLE
omm=#

--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

omm=# 

--或直接查看约束是否被删除
omm=# select * from pg_constraint  where conname like 'test_pkey';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | confdeltype | confmatchtype 
| conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-------------+---------------
+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+--------+--------+--------------
(0 rows)

omm=#

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：
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=# 

--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 | confdeltype | confmatchtyp
e | 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=# \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=#

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
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

omm=#

7.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

omm=#

8.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

omm=#

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：
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=#

10.删除表

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

课程作业

1.创建表，为表添加字段

omm=# drop table if exists lxs;
DROP TABLE
omm=# create table lxs(
omm(#     id int,
omm(#     info varchar2(20),
omm(#     name text not null,
omm(#     primary key(id)
omm(# );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "lxs_pkey" for table "lxs"
CREATE TABLE
omm=# \d lxs
             Table "public.lxs"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | integer               | not null
 info   | character varying(20) | 
 name   | text                  | not null
Indexes:
    "lxs_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# alter table lxs add column age int;
ALTER TABLE
omm=#

2.删除表中的已有字段

omm=# alter table lxs drop column info  ;
ALTER TABLE
omm=# \d lxs
      Table "public.lxs"
 Column |  Type   | Modifiers 
--------+---------+-----------
 id     | integer | not null
 name   | text    | not null
 age    | integer | 
Indexes:
    "lxs_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=#

3.删除表的已有约束、添加约束

omm=# alter table lxs drop constraint lxs_pkey;
ALTER TABLE
omm=# \d lxs
      Table "public.lxs"
 Column |  Type   | Modifiers 
--------+---------+-----------
 id     | integer | not null
 name   | text    | not null
 age    | integer | 

omm=# \x
Expanded display is off.
omm=# select * from pg_constraint  where conname like 'lxs_pkey';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | confdeltype | confmatchtype 
| conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-------------+---------------
+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+--------+--------+--------------
(0 rows)

omm=#
omm=# alter table lxs add constraint pk_lyp_id primary key(id);
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index "pk_lyp_id" for table "lxs"
ALTER TABLE
omm=#
omm=# select * from pg_constraint  where conname like 'pk_lyp_id';
  conname  | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | confdeltype | confmatchtyp
e | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | consrc | conincluding 
-----------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-------------+-------------
--+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+--------+--------+--------------
 pk_lyp_id |         2200 | p       | f             | f           | t            |    16433 |        0 |    16441 |         0 |             |             |             
  | t          |           0 | t            | f       | f      | {1}    |         |           |           |           |           |        |        | 
(1 row)

omm=# 
omm=# \d lxs
      Table "public.lxs"
 Column |  Type   | Modifiers 
--------+---------+-----------
 id     | integer | not null
 name   | text    | not null
 age    | integer | 
Indexes:
    "pk_lyp_id" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# \x
Expanded display is on.
omm=#

4.修改表字段的默认值

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

omm=#

5.修改表字段的数据类型

omm=# alter table lxs ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# \d lxs 
      Table "public.lxs"
 Column |  Type   | Modifiers  
--------+---------+------------
 id     | integer | not null
 name   | text    | not null
 age    | bigint  | default 20
Indexes:
    "pk_lyp_id" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=#

6.修改表字段的名字

omm=# ALTER TABLE lxs RENAME COLUMN age TO oldage;
ALTER TABLE
omm=# \d lxs 
      Table "public.lxs"
 Column |  Type   | Modifiers  
--------+---------+------------
 id     | integer | not null
 name   | text    | not null
 oldage | bigint  | default 20
Indexes:
    "pk_lyp_id" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=#

7.修改表的名字

omm=# ALTER TABLE lxs RENAME TO llllxs;
ALTER TABLE
omm=# \d llllxs
omm=#      Table "public.llllxs"
 Column |  Type   | Modifiers  
--------+---------+------------
 id     | integer | not null
 name   | text    | not null
 oldage | bigint  | default 20
Indexes:
    "pk_lyp_id" PRIMARY KEY, btree (id) TABLESPACE pg_default


omm=#

8.删除表

omm=# DROP TABLE llllxs;
DROP TABLE
omm=# \d
No relations found.
omm=#

–学如逆水行舟，不进则退。

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