mysql ---范式的学习

Posted 2020-12-17 正霜霜儿

--数据库的三大范式 ，sql

--1.第一范式
--1NF
--数据表中的所有字段都是不可分割的原子值

create table student2(
id int primary key,
name varchar(20),
address varchar(30)
);

mysql> insert into student2 values(1,"xiaozhan","chongqing");
Query OK, 1 row affected (0.01 sec)

mysql> insert into student2 values(2,"wangyibo","henan");
Query OK, 1 row affected (0.00 sec)

mysql> insert into student2 values(3,"wanghan","hunan");
Query OK, 1 row affected (0.01 sec)

mysql> select * from student2;
+----+----------+-----------+
| id | name | address |
+----+----------+-----------+
| 1 | xiaozhan | chongqing |
| 2 | wangyibo | henan |
| 3 | wanghan | hunan |
+----+----------+-----------+
3 rows in set (0.00 sec)

mysql>

----字段值还可以继续拆分的，就不满足第一范式。


create table student3(
id int primary key,
name varchar(20),
country varchar(30),
privence varchar(30),
city varchar(30),
details varchar(30)
);


mysql> desc student3;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int | NO | PRI | NULL | |
| name | varchar(20) | YES | | NULL | |
| country | varchar(30) | YES | | NULL | |
| privence | varchar(30) | YES | | NULL | |
| city | varchar(30) | YES | | NULL | |
| details | varchar(30) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

 


insert into student3 values(1,"zhangsan","中国","江苏","南京","江宁区");

insert into student3 values(1,"zhangsan","中国","江苏","南京","溧水");

insert into student3 values(1,"zhangsan","中国","湖北","十堰","竹溪");

mysql> insert into student3 values(2,"zhangsan","中国","湖北","十堰","竹溪");
Query OK, 1 row affected (0.00 sec)

mysql> insert into student3 values(3,"zhangsan","中国","江苏","南京","溧水");
Query OK, 1 row affected (0.00 sec)

mysql> select * from student3;
+----+----------+---------+----------+--------+-----------+
| id | name | country | privence | city | details |
+----+----------+---------+----------+--------+-----------+
| 1 | zhangsan | 中国 | 江苏 | 南京 | 江宁区 |
| 2 | zhangsan | 中国 | 湖北 | 十堰 | 竹溪 |
| 3 | zhangsan | 中国 | 江苏 | 南京 | 溧水 |
+----+----------+---------+----------+--------+-----------+
3 rows in set (0.00 sec)

mysql>

---范式，设计的越详细，对于某些实际操作可能更好，但是不一定都是好处。
---范式的设计根据实际的项目的开发设定，不一定非得满足某个特定的范式


---2.第二范式

---必须是满足第一范式下的前提下，第二范式要求，除主键外的每一列都必须完全依赖于主键，
---如果要出现不完全依赖，只可能发生在联合组建的情况下。

---订单表

create table myorder(
product_id int,
customer_id int,
product_name varchar(20),
customer_name varchar(20),
primary key(product_id,customer_id)
);


---问题

---除主键以外的其他例，只依赖与主键的部分字段。
--拆表。
create table myorder(
order_id int primary key,
product_id int,
customer_id int 
);

create table product(
id int primary key,
name varchar(20)
);

create table customer(
id int primary key,
name varchar(20),

);


---分成三个表之后，就满足了第二范式的设计。

---第三范式：
---3nf
---必须先满足第二范式，除开主键列的其他列之间不能有传递依赖关系。
create table myorder(
order_id int primary key,
product_id int,
customer_id int,
);


create table product(
id int primary key,
name varchar(20)
);

create table customer(
id int primary key,
name varchar(20),
customer_phone varchar(15)
);