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首页 / openGuass每日一练第14天|学习心得体会

openGuass每日一练第14天|学习心得体会

原创 小严 2022-12-07
234

课程学习内容

软件版本 ：openGauss 3.0.0

学习表的约束、表的默认值、自增类型等技术

数据库实操内容

环境准备

su - omm

gsql -r

root@modb:~# su - omm
omm@modb:~$ gsql -r
gsql ((openGauss 3.0.0 build 02c14696) compiled at 2022-04-01 18:12:00 commit 0 last mr  )
Non-SSL connection (SSL connection is recommended when requiring high-security)
Type "help" for help.

omm=#

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）。

drop table if exists test; create table test( id bigint primary key, name varchar(50) not null, age int );

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(#   age  int
omm(# 	);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE

–插入数据

insert into test values(1,‘user1’,50);

omm=# insert into test values(1,'user1',50);
INSERT 0 1

–查看数据

select * from test;

omm=# select * from test;
 id | name  | age 
----+-------+-----
  1 | user1 |  50
(1 row)

–查看约束

\d test

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=#

创建表的时候定义表级约束

–创建表时定义表级约束 执行下面的SQL语句，在创建表的时候为表定义表级约束：

#这里在表列级定义了primary key约束（id列），在列级定义了not null约束（name列）。

drop table if exists test001;

create table test001(

id bigint,

name varchar(50) not null, – 创建列级not null约束

age int,

primary key(id) – 创建表级约束

​ );

insert into test001 values(1,‘user1’,50);

select * from test001;

\d test001

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;
omm=#  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=#

为表的属性定义默认值

–执行下面的语句，在创建表的时候为表的某个列定义默认值：

drop table if exists test002;

create table test002(

id bigint,

name varchar(28) not null,

age int default 20, – 为该列定义默认值为20

primary key(id)

​ );

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(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test002_pkey" for table "test002"
CREATE TABLE
omm=#

–下面的SQL insert语句，在向表test插入数据时，没有提供age列的值：

insert into test002(id,name) values(1,‘user1’);

insert into test002(id,name) values(2,‘user2’);

select * from test002;

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=#

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

drop table if exists test;

create table test(

id bigint,

name varchar(50) not null,

age int,

primary key(id)

​ );

insert into test(id,name) values(1,‘user1’);

select * from test;

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)


omm=#

创建表时使用自增数据类型

商品的发piao（票）编号通常按顺序递增。这种情况可以使用serial数据类型。最简单方法直接使用serial数据类型。

-创建一个带有serial数据类型的测试表invoice：

drop table if exists invoice;

create table invoice(invoicenum serial NOT NULL,name varchar(20));

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

–为表invoice插入3条记录，并查看插入数据后的表的数据：

insert into invoice(name) values(‘user1’);

insert into invoice(name) values(‘user2’);

insert into invoice(name) values(‘user3’);

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=#

–可以看到每插入一条记录到表invoice后，列invoicenum的值会自增1。

select * from invoice;

omm=# select * from invoice;
 invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3
(3 rows)

omm=#

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：

DROP TABLE if exists newtestwithdata;

CREATE TABLE newtestwithdata AS SELECT * FROM invoice;

SELECT * FROM newtestwithdata;

omm=#  DROP TABLE if exists newtestwithdata;
NOTICE:  table "newtestwithdata" does not exist, skipping
DROP TABLE
omm=#  CREATE TABLE newtestwithdata AS SELECT * FROM invoice;
INSERT 0 3
omm=#  SELECT * FROM newtestwithdata;
 invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3
(3 rows)

omm=#

–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：

DROP TABLE if exists testnewwithoutdata;

CREATE TABLE testnewwithoutdata AS SELECT * FROM invoice WHERE 1=2;

SELECT * FROM testnewwithoutdata;

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=#

课程作业

创建表的时候定义列级约束

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

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

omm=#

创建表的时候定义表级约束

omm=# drop table if exists testdb1;
DROP TABLE
omm=# NOTICE:  table "testdb1" does not exist, skipping

omm=# create table testdb1(
omm(#       id bigint,
omm(#       age  int,
omm(#       name varchar(50) not null,  -- 创建列级not null约束
omm(#       primary key(id) -- 创建表级约束
omm(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "testdb1_pkey" for table "testdb1"
CREATE TABLE
omm=# insert into testdb1 values(1,'user1',50);
INSERT 0 1
omm=# select * from testdb1;
 id | name  | age 
----+-------+-----
  1 | user1 |  50
(1 row)

omm=# \d testdb1
           Table "public.testdb1"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | 
Indexes:
    "testdb1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=#

为表的属性定义默认值

omm=# drop table if exists testdb2;
NOTICE:  table "testdb2" does not exist, skipping
DROP TABLE
omm=# create table testdb2(
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 "testdb2_pkey" for table "testdb2"
CREATE TABLE
omm=# insert into testdb2(id,name) values(1,'user1');
INSERT 0 1
omm=# insert into testdb2(id,name) values(2,'user2');
INSERT 0 1
omm=# select * from testdb2;
 id | name  | age 
----+-------+-----
  1 | user1 |  20
  2 | user2 |  20
(2 rows)

omm=#

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 test11;
NOTICE:  table "test11" does not exist, skipping
DROP TABLE
omm=# create table test11(
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 "test11_pkey" for table "test11"
CREATE TABLE
omm=# insert into test11(id,name) values(1,'user1');
INSERT 0 1
omm=# select * from test11;
 id | name  | age 
----+-------+-----
  1 | user1 |    
(1 row)

omm=#

创建表时使用自增数据类型

omm=# drop table if exists invoice1;
NOTICE:  table "invoice1" does not exist, skipping
DROP TABLE
omm=# create table invoice1(invoicenum serial NOT NULL,name varchar(20));
NOTICE:  CREATE TABLE will create implicit sequence "invoice1_invoicenum_seq" for serial column "invoice1.invoicenum"
CREATE TABLE
omm=# insert into invoice1(name) values('user1');
INSERT 0 1
omm=# insert into invoice1(name) values('user2');
INSERT 0 1
omm=# insert into invoice1(name) values('user3');
INSERT 0 1
omm=# select * from invoice1;
 invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3
(3 rows)

omm=#

使用现有的表创建新表

omm=# DROP TABLE if exists newtestwithdata1;
NOTICE:  table "newtestwithdata1" does not exist, skipping
DROP TABLE
omm=# CREATE TABLE newtestwithdata1 AS SELECT * FROM invoice1;
INSERT 0 3
omm=# SELECT * FROM newtestwithdata1;
 invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3
(3 rows)

omm=# DROP TABLE if exists newtestwithdata1;
DROP TABLE
omm=# CREATE TABLE newtestwithdata1 AS SELECT * FROM invoice WHERE 1=2;
INSERT 0 0
omm=# SELECT * FROM newtestwithdata1;
 invoicenum | name 
------------+------
(0 rows)

omm=#

课程学习体会
​ 通过本次的实训操作，掌握创建数据库表的约束、表的默认值、自增类型以及使用现有的表创建新表。

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