openGauss每日一练第14天 | 学习心得体会

1.创建表的时候定义列级约束

NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=# 

2.创建表的时候定义表级约束

NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test001_pkey" for table "test001"
CREATE TABLE
omm=# 

3.为表的属性定义默认值

CREATE TABLE
omm=# insert into test002 values(1);
INSERT 0 1
omm=# select * from test002;
 id | age 
----+-----
  1 |  20
(1 row)

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=# CREATE TABLE

omm=# insert into test003 values(2);
INSERT 0 1
omm=# select * from test003;
(1 row)

omm=#  id | age | sex 
----+-----+-----
  2 |  20 | 

5.创建表时使用自增数据类型

NOTICE:  CREATE TABLE will create implicit sequence "test004_invoicenum_seq" for serial column "test004.invoicenum"
CREATE TABLE
omm=# insert into test004(name) values ('xiaoming');
INSERT 0 1
omm=# insert into test004(name) values ('xiaohong');
INSERT 0 1
omm=# select * from test004;
          2 | xiaohong
(2 rows)

omm=#  invoicenum |   name   
------------+----------
          1 | xiaoming

6.使用现有的表创建新表

INSERT 0 2
omm=# insert into new_test004 select * from test004;
omm=# INSERT 0 2

omm=# select * from new_test004;
 invoicenum |   name   
------------+----------
          1 | xiaoming
          2 | xiaohong
(4 rows)