openGauss每日一练第14天 | openGauss逻辑结构：表管理2

原创闫龙伟 2022-12-07

186

课程作业

1.创建表的时候定义列级约束

-- 创建表的时候为表定义列级约束：在列级定义了primary key约束（id列）和not null约束（name列）。

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

omm=# --查看约束
omm=# \d test 
        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=# 
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2.创建表的时候定义表级约束

omm=# drop table if exists test001;
NOTICE:  table "test001" does not exist, skipping
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=# 
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3.为表的属性定义默认值

omm=# drop table if exists test002;
NOTICE:  table "test002" does not exist, skipping
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(# insert into test002(id,name) values(1,'user1');
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test002_pkey" for table "test002"
CREATE TABLE
INSERT 0 1
omm=# insert into test002(id,name) values(2,'user2');
INSERT 0 1
omm=# 
omm=#   select * from test002;
(2 rows)

omm=#  id | name  | age 
----+-------+-----
 1 | user1 |  20
 2 | user2 |  20
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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

-- 未定义age列的默认值，如果插入数据时未提供该列的值，则将默认插入空值null
omm=# drop table if exists test;
DROP TABLE
omm=#  create table test(
omm(#        id bigint,
omm(# omm(#         name varchar(50) not null,
  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;
 id | name  | age 
----+-------+-----
  1 | user1 |    
(1 row)

omm=# 
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5.创建表时使用自增数据类型

omm=# drop table if exists invoice;
NOTICE:  table "invoice" does not exist, skipping
DROP TABLE
--创建一个带有serial数据类型的测试表invoice：
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"
omm=# 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
--可以看到每插入一条记录到表invoice后，列invoicenum的值会自增1。
omm=# select * from invoice;
invoicenum | name  
------------+-------
      1 | user1
      2 | user2
      3 | user3
(3 rows)

omm=# 
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6.使用现有的表创建新表

--执行下面的SQL语句，将创建新表，并且会将旧表的数据拷贝给新表：
omm=# DROP TABLE if exists newtestwithdata;
NOTICE:  table "newtestwithdata" does not exist, skipping
omm=# DROP TABLE
CREATE TABLE newtestwithdata AS SELECT * FROM invoice;
INSERT 0 3
omm=#  SELECT * FROM newtestwithdata;
(3 rows)

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


--执行下面的SQL语句，创建和旧表的表结构相同的新表，但是不会将旧表的数据拷贝给新表：
omm=# DROP TABLE if exists testnewwithoutdata;
NOTICE:  table "testnewwithoutdata" does not exist, skipping
DROP TABLE
omm=#  CREATE TABLE testnewwithoutdata AS SELECT * FROM invoice WHERE 1=2;
INSERT 0 0
omm=#  SELECT * FROM testnewwithoutdata;
invoicenum | name 
------------+------
(0 rows)

omm=# 复制