openGauss每日一练第16天| openGauss逻辑结构：表管理

课程作业

1.创建表，为表添加字段

omm=# drop table if exists test;
DROP TABLE
--创建新表
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
omm=# 
omm=# \dt
                        List of relations
 Schema | Name | Type  | Owner |             Storage              
--------+------+-------+-------+----------------------------------
 public | test | table | omm   | {orientation=row,compression=no}
(1 row)

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
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--为表添加字段sex 
omm=# alter table test add column sex Boolean;
ALTER TABLE
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=# 
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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
omm=# 
--执行下面gsql命令，再次查看表test的信息
omm=# \d test
 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=# 
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3.删除表的已有约束、添加约束

--删除表的已有约束
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

omm=# 
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--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=# \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=# 
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4.修改表字段的默认值

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=# 
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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

omm=# 
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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

omm=# 
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7.修改表的名字

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=# 
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8.删除表

DROP TABLE mytest;
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