openGauss每日一练第14天| openGauss逻辑结构：表管理

课程作业

1.创建表的时候定义列级约束

omm=#   drop table if exists test;
DROP TABLE
omm=#   create table test(
omm(#        id bigint primary key, 
omm(#        name varchar(50) not null,
omm(#        age  int
omm(#        );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=# 
omm=#   insert into test values(1,'user1',50);
INSERT 0 1
omm=# 
omm=#  select * from test;
omm=#  id | name  | age 
----+-------+-----
  1 | user1 |  50
(1 row)
omm=# \d test 
omm=#             Table "public.test"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 

2.创建表的时候定义表级约束

omm=# drop table if exists test001;
DROP TABLE
omm=# create table test001(
omm(#       id bigint,
omm(#       name varchar(50) not null,  -- 创建列级not null约束
omm(#       age  int,
omm(#       primary key(id) -- 创建表级约束
omm(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test001_pkey" for table "test001"
CREATE TABLE
omm=# insert into test001 values(1,'user1',50);
INSERT 0 1
omm=# select * from test001;
 id | name  | age 
----+-------+-----
  1 | user1 |  50
(1 row)

omm=# \d test001
           Table "public.test001"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | 
Indexes:
    "test001_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 

3.为表的属性定义默认值

omm=# drop table if exists test002;
DROP TABLE
omm=# create table test002(
omm(#       id bigint,
omm(#       name varchar(28) not null,
omm(#       age  int default 20,  --  为该列定义默认值为20
omm(#       primary key(id)
omm(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test002_pkey" for table "test002"
CREATE TABLE
omm=# 
omm=# insert into test002(id,name) values(1,'user1');
INSERT 0 1
omm=# insert into test002(id,name) values(2,'user2');
INSERT 0 1
omm=# 
  select * from test002;
 id | name  | age 
----+-------+-----
  1 | user1 |  20
  2 | user2 |  20
(2 rows)
omm=# 

4.如果在创建表的时候，没有为某列定义默认值，缺省的默认值是空值null

omm=#  drop table if exists test;
DROP TABLE
omm=#  create table test(
omm(#         id bigint,
omm(#         name varchar(50) not null,
omm(#         age  int,                                
omm(#         primary key(id)
omm(#        );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=#  insert into test(id,name) values(1,'user1');
INSERT 0 1
omm=#  select * from test;
omm-# 
 id | name  | age 
----+-------+-----
  1 | user1 |    
(1 row)

5.创建表时使用自增数据类型

omm=# drop table if exists invoice;
DROP TABLE
omm=# create table invoice(invoicenum serial NOT NULL,name varchar(20));
NOTICE:  CREATE TABLE will create implicit sequence "invoice_invoicenum_seq" for serial column "invoice.invoicenum"
CREATE TABLE
omm=#  insert into invoice(name) values('user1');
INSERT 0 1
omm=# insert into invoice(name) values('user2');
INSERT 0 1
omm=# insert into invoice(name) values('user3');
INSERT 0 1
omm=# select * from invoice;
(3 rows)

omm=#  invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3

omm=# 

6.使用现有的表创建新表

omm=# --按照test表结构创建新表test1，并将数据完全复制过去
omm=#  CREATE TABLE test_1 AS SELECT * FROM test;
INSERT 0 1
omm=#  SELECT * FROM test_1;
 id | name  | age 
----+-------+-----
  1 | user1 |    
(1 row)

omm=# 
omm=# --按照test表结构创建新表test1，仅复制表结构
omm=#  CREATE TABLE test_2 AS SELECT * FROM test  WHERE 1=2;
INSERT 0 0
omm=#  SELECT * FROM test_2;
 id | name | age 
----+------+-----
(0 rows)

omm=#