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

学习目标

学习表的约束、表的默认值、自增类型等技术

课程学习

1.创建表的时候定义列级约束

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.-- 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=# 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"
omm=# CREATE TABLE--插入数据、查看数据、查看约束
omm=# insert into test values(1,'user1',50);
INSERT 0 1
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

2.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）。
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"
omm=# 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
omm=#            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

3.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：
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--下面的SQL insert语句，在向表test插入数据时，没有提供age列的值：
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=# 
omm=# select * from test002;
omm=#  id | name  | age 
----+-------+-----
  1 | user1 |  20
  2 | user2 |  20
(2 rows)

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)

5.创建表时使用自增数据类型
商品清单的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：
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--为表invoice插入3条记录，并查看插入数据后的表的数据：
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)

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
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)
--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)
--WHERE 后面表示过滤的条件，只有满足条件的记录才被选择，因为条件（1=2）为假，其实就是什么都不选择，查询不会返回数据，如果条件是“1=1”就是选择所有记录。

课程作业

1.创建表的时候定义列级约束

omm=# drop table if exists xx1;
NOTICE:  table "xx1" does not exist, skipping
DROP TABLE
omm=# create table xx1(
omm(# id bigint primary key, 
omm(#  name varchar(50) not null,
omm(# age  int
omm(#        );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "xx1_pkey" for table "xx1"
omm=# CREATE TABLE
omm=#  insert into  xx1 values(1,'user1',50);
INSERT 0 1
omm=# select  * from xx1 ;
 id | name  | age 
----+-------+-----
  1 | user1 |  50
(1 row)

omm=# \d xx1
             Table "public.xx1"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | 
Indexes:
    "xx1_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

2.创建表的时候定义表级约束

omm=# drop table if exists xx2;
NOTICE:  table "xx2" does not exist, skipping
DROP TABLE
omm=# create table xx2(
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 "xx2_pkey" for table "xx2"
CREATE TABLE
omm=# insert into xx2 values (1,'user1',50);
INSERT 0 1
omm=# select * from xx2;
 id | name  | age 
----+-------+-----
  1 | user1 |  50
(1 row)

omm=# \d xx2
             Table "public.xx2"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | 
Indexes:
    "xx2_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

3.为表的属性定义默认值

omm=# drop table if exists xx3;
NOTICE:  table "xx3" does not exist, skipping
omm=# DROP TABLE

omm=# create table xx3(
omm(#       id bigint,
omm(#       name varchar(28) not null,
omm(#       age  int default 20, 
omm(#       primary key(id)
omm(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "xx3_pkey" for table "xx3"
CREATE TABLE
omm=# insert into xx3(id,name) values (1,'user1');
INSERT 0 1
omm=# insert into xx3(id,name) values (2,'user2');
INSERT 0 1
omm=# select * from xx3;
 id | name  | age 
----+-------+-----
  1 | user1 |  20
  2 | user2 |  20
(2 rows)

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 xx4;
NOTICE:  table "xx4" does not exist, skipping
DROP TABLE
omm=# create table xx4(
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 "xx4_pkey" for table "xx4"
CREATE TABLE
omm=# insert into xx4(id,name) values (1,'user1');
INSERT 0 1
omm=# select * from xx4;
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 xx5;
NOTICE:  table "xx5" does not exist, skipping
DROP TABLE
omm=# create  table xx5(invoicenum serial not null,name varchar(20));
NOTICE:  CREATE TABLE will create implicit sequence "xx5_invoicenum_seq" for serial column "xx5.invoicenum"
CREATE TABLE
omm=# insert into xx5(name) values ('user1');
INSERT 0 1
omm=# insert into xx5(name) values ('user2');
INSERT 0 1
omm=# insert into xx5(name) values ('user3');
INSERT 0 1
omm=# select * from xx5;
 invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3
(3 rows)

6.使用现有的表创建新表

omm=# drop table if exists xx6;
NOTICE:  table "xx6" does not exist, skipping
DROP TABLE
omm=# create table xx6 as select * from xx5;
INSERT 0 3
omm=# select * from xx6;
 invoicenum | name  
------------+-------
          1 | user1
          2 | user2
          3 | user3
(3 rows)
omm=# drop table if exists xx7;
NOTICE:  table "xx7" does not exist, skipping
DROP TABLE
omm=# create table xx7 as select * from xx5 where 1=2;
INSERT 0 0
omm=# select * from xx7;
 invoicenum | name 
------------+------
(0 rows)