Mysql表的約束設計和關聯關係設計

https://blog.csdn.net/u012750578/article/details/15026677

Mysql表的約束設計和關聯關係設計

======================表的完整性======================

  (1)實體完整性：每條記錄有一個惟一標識符，一般用無任何業務含義的字段表示(主鍵)

  (2)參照完整性：一張表的某個字段必須引用另外一張表的某個字段值(外鍵)

  (3)域完整性：域即單元數據，域中的數值必須符合必定的規則

定義主鍵約束

  primary key:不容許爲空，不容許重複

刪除主鍵：alter table tablename drop primary key ;

 

定義主鍵自動增加(id,沒有業務含義)

    auto_increment(MySQL特有/UUID類生成)

定義惟一約束

  unique

定義非空約束

  not null

定義外鍵約束

constraint ordersid_FKforeign key(ordersid) references orders(id),

2 鍵的概念

  (1)主鍵：只有惟一字段

  (2)組合主鍵：由多個字段組合起來，造成惟一字段

  (3)外鍵：針對多張表之間的關聯

 

3 主鍵的特色

  (1)主鍵不能重複

  (2)主鍵不能爲NULL

  (3)auto_increment是MySQL特有的，默認從1開始，該ID值與表同生亡

  (4)多人項目中，一般使用UUID來生成惟一的主鍵值，便於多個合併數據時依然保持實體完整性

--id主鍵

mysql> create table teacher(id intprimary key,

   -> name varchar(20),

   -> brithday date);

Query OK, 0 rows affected (0.61 sec)

 

mysql> select * from teacher;

Empty set (0.00 sec)

 

mysql> insert into teachervalues(1,'jack','1992-2-12');

Query OK, 1 row affected (0.11 sec)

 

mysql> select * from teacher;

+----+------+------------+

| id | name | brithday   |

+----+------+------------+

|  1| jack | 1992-02-12 |

+----+------+------------+

1 row in set (0.00 sec)

 

mysql> desc teacher;

+----------+-------------+------+-----+---------+-------+

| Field   | Type        | Null | Key |Default | Extra |

+----------+-------------+------+-----+---------+-------+

| id      | int(11)     | NO   | PRI | NULL    |      |

| name    | varchar(20) | YES  |     | NULL   |       |

| brithday | date        | YES |     | NULL    |      |

+----------+-------------+------+-----+---------+-------+

3 rows in set (0.00 sec)

--主鍵不能重複,主鍵衝突,1表明第一列，即id列

mysql> insert into teachervalues(1,'marry','1996-2-12');

ERROR 1062 (23000): Duplicate entry '1' forkey 'PRIMARY'

mysql>

--主鍵不能爲null

mysql> insert into teachervalues(null,'marry','1996-2-12');

ERROR 1048 (23000): Column 'id' cannot benull

-- 刪除主鍵，主鍵在表只有一個，要麼是一列，要麼是多列

mysql> alter table teacher drop primarykey;

Query OK, 1 row affected (2.13 sec)

Records: 1 Duplicates: 0  Warnings: 0

 

mysql> desc teacher;

+----------+-------------+------+-----+---------+-------+

| Field   | Type        | Null | Key |Default | Extra |

+----------+-------------+------+-----+---------+-------+

| id      | int(11)     | NO   |    | NULL    |       |

| name    | varchar(20) | YES  |     | NULL   |       |

| brithday | date        | YES |     | NULL    |      |

+----------+-------------+------+-----+---------+-------+

3 rows in set (0.01 sec)

--主鍵id自動增加

mysql> drop table if exists teacher;

Query OK, 0 rows affected (0.32 sec)

mysql> create table teacher(id intprimary key auto_increment,

   -> name varchar(20),

   -> birthday date);

Query OK, 0 rows affected (0.96 sec)

mysql> desc teacher;

+----------+-------------+------+-----+---------+----------------+

| Field   | Type        | Null | Key |Default | Extra          |

+----------+-------------+------+-----+---------+----------------+

| id      | int(11)     | NO   | PRI | NULL    | auto_increment |

| name    | varchar(20) | YES  |     | NULL   |                |

| birthday | date        | YES |     | NULL    |                |

+----------+-------------+------+-----+---------+----------------+

3 rows in set (0.01 sec)

mysql> insert into teacher(name,birthday)values('jack','1992-02-12');

Query OK, 1 row affected (0.06 sec)

 

mysql> insert intoteacher(name,birthday) values('marry','1992-4-8');

Query OK, 1 row affected (0.09 sec)

 

mysql> insert intoteacher(name,birthday) values('arry','1982-4-8');

Query OK, 1 row affected (0.14 sec)

 

mysql> select * from teacher;

+----+-------+------------+

| id | name | birthday   |

+----+-------+------------+

|  1| jack  | 1992-02-12|

|  2| marry | 1992-04-08 |

|  3| arry  | 1982-04-08|

+----+-------+------------+

3 rows in set (0.00 sec)

--檢查主鍵id增加的序列

mysql> delete from teacher whereid<=3;

Query OK, 3 rows affected (0.08 sec)

 

mysql> select * from teacher;

Empty set (0.00 sec)

 

mysql> insert intoteacher(name,birthday) values('jack','1992-02-12');

Query OK, 1 row affected (0.13 sec)

 

mysql> select * from teacher;

+----+------+------------+

| id | name | birthday   |

+----+------+------------+

|  4| jack | 1992-02-12 |

+----+------+------------+

1 row in set (0.00 sec)

--多人項目中，一般使用UUID來生成惟一的主鍵值，便於多個合併數據時依然保持實體完整性

 

4 惟一約束的特色

  (1)非NULL值不能重複

  (2)能夠插入多個NULL值

  (3)'NULL'空串和NULL是不一樣的概念

mysql> drop table teacher;

Query OK, 0 rows affected (0.42 sec)

--惟一

mysql> create table teacher(id intprimary key auto_increment,

   -> name varchar(20) unique,

   -> birthday date);

Query OK, 0 rows affected (1.49 sec)

 

mysql> insert intoteacher(name,birthday) values('marry','2011-2-2');

Query OK, 1 row affected (0.11 sec)

 

mysql> insert intoteacher(name,birthday) values(NULL,'2011-1-1');

Query OK, 1 row affected (0.04 sec)

 

mysql> desc teacher;

+----------+-------------+------+-----+---------+----------------+

| Field   | Type        | Null | Key |Default | Extra          |

+----------+-------------+------+-----+---------+----------------+

| id      | int(11)     | NO   | PRI | NULL    | auto_increment |

| name    | varchar(20) | YES  | UNI | NULL   |                |

| birthday | date        | YES |     | NULL    |                |

+----------+-------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

--違反惟一

mysql> insert intoteacher(name,birthday) values('marry','2011-2-2');

ERROR 1062 (23000): Duplicate entry 'marry'for key 'name'

5 非空約束特色

  (1)不能插入NULL值

  (2)主鍵約束=非NULL約束+惟一約束

--違返不爲空約束

mysql> drop table if exists teacher;

Query OK, 0 rows affected (0.19 sec)

 

mysql> create table teacher(

   ->    id int primary keyauto_increment,

   ->    name varchar(20) not nullunique,

   ->    birthday date

   -> );

Query OK, 0 rows affected (1.45 sec)

 

mysql> insert intoteacher(name,birthday) values(NULL,'2011-1-1');

ERROR 1048 (23000): Column 'name' cannot benull

6 外健特色

  (1)外鍵值必須來源於所引用別一個表主鍵值，或NULL

  

*7 關聯關係

  (1)一對一(外健根業務有關) 

  (2)一對多或多對一(外鍵放置在多方)

  (3)多對多(外健放置在關聯表中，即將一個多對多拆分紅二個一對多關係)

一對一關係一:

mysql> create table person(

   ->  id int primary keyauto_increment,

   ->  name varchar(20) not null

   -> );

Query OK, 0 rows affected (1.16 sec)

mysql> insert into person(name)values('jack');

Query OK, 1 row affected (0.15 sec)

 

mysql> insert into person(name)values('marry');

Query OK, 1 row affected (0.06 sec)

--card中pid爲外person的外鍵

mysql> create table card(

    -> id int primary key auto_increment,

   ->  location varchar(20) notnull,

   ->  pid int,

   ->  constraint pid_FK foreignkey(pid) references person(id)

   -> );

Query OK, 0 rows affected (1.55 sec)

mysql> insert into card(location,pid)values('BJ',1);

Query OK, 1 row affected (0.11 sec)

 

mysql> insert into card(location,pid)values('GZ',2);

Query OK, 1 row affected (0.39 sec)

--外鍵pid能夠插入NULL

mysql> insert into card(location,pid)values('CS',NULL);

Query OK, 1 row affected (0.05 sec)

--顯示person與card表中的數據

mysql> select * from person;

+----+-------+

| id | name |

+----+-------+

|  1| jack  |

|  2| marry |

+----+-------+

2 rows in set (0.00 sec)

 

mysql> select * from card;

+----+----------+------+

| id | location | pid  |

+----+----------+------+

|  1| BJ       |    1 |

|  2| GZ       |    2 |

|  3| CS       | NULL |

+----+----------+------+

3 rows in set (0.00 sec)

--插入pid爲3的出錯誤，外鍵pid必須來源另外一表的主鍵值或爲NULL

mysql> insert into card(location,pid)values('NJ',3);

ERROR 1452 (23000): Cannot add or update achild row: a foreign key constraint fails (`mydb2`.`card`, CONSTRAINT `pid_FK`FOREIGN KEY (`pid`) REFERENCES `person` (`id`))

注意:外鍵值必須來源於所引用別一個表主鍵值，或NULL  

--有外鍵關係的行不能刪除，需先刪除其關聯的外鍵關係,再進行刪除主鍵關係的數據，與建立的時候相反      

mysql> deletefrom person where name='jack';

ERROR 1451(23000): Cannot delete or update a parent row: a foreign key constraint fails(`mydb2`.`card`, CONSTRAINT `pid_FK` FOREIGN KEY (`pid`) REFERENCES `person`(`id`))

一對一關係方式二:主鍵看成另外一個表的外鍵

例下面的card表的id既是主鍵又是外鍵

mysql> drop table if exists card;

Query OK, 0 rows affected (0.22 sec)

 

mysql> drop table if exists person;

Query OK, 0 rows affected (0.22 sec)

 

mysql> create table person(

    -> id int primary key auto_increment,

   ->  name varchar(20) not null

   -> );

Query OK, 0 rows affected (0.90 sec)

 

mysql> insert into person(name)values('jack');

Query OK, 1 row affected (0.07 sec)

 

mysql> insert into person(name)values('marry')

   -> ;

Query OK, 1 row affected (0.10 sec)

--使用主鍵做爲外鍵

mysql> create table card(

   ->  id int primary keyauto_increment,

   ->  location varchar(20) notnull,

   ->  constraint id_FK foreignkey(id) references person(id)

   -> );

Query OK, 0 rows affected (0.86 sec)

 

mysql> insert into card(location)values('BJ');

Query OK, 1 row affected (0.06 sec)

mysql> insert into card(location)values('CS');

Query OK, 1 row affected (0.18 sec);

--id爲3, 不符合參照完整性,3在person表中打不到

mysql> insert into card(location) values('GZ');

ERROR 1452 (23000): Cannot add or update achild row: a foreign key constraint fails (`mydb2`.`card`, CONSTRAINT `id_FK`FOREIGN KEY (`id`) REFERENCES `person` (`id`))

--NULL也不行，由於這裏id爲一個非空的屬性

mysql> insert into card(location)values(NULL);

ERROR 1048 (23000): Column 'location'cannot be null

==========================一對多關係=============================

設計方案:

一方作一個容器，多方作一個引用

mysql> create table department(

   ->  id int primary keyauto_increment,

   ->  name varchar(20) not null

   -> );

Query OK, 0 rows affected (1.70 sec)

 

mysql> insert into department(name)values('軟件部');

Query OK, 1 row affected (0.10 sec)

 

mysql> insert into department(name)values('銷售部');

Query OK, 1 row affected (0.06 sec)

 

mysql> create table employee(

   ->  id int primary keyauto_increment,

   ->  name varchar(20) not null,

   ->  did int,

   ->  constraint did_FK foreignkey(did) references department(id)

   -> );

Query OK, 0 rows affected (1.02 sec)

 

mysql> insert into employee(name,did)values('jack',1);

Query OK, 1 row affected (0.12 sec)

 

mysql> insert into employee(name,did)values('marry',1);

Query OK, 1 row affected (0.13 sec)

 

mysql>

 

mysql> select * from department;

+----+-----------+

| id | name      |

+----+-----------+

|  1| 軟件部    |

|  2| 銷售部    |

+----+-----------+

2 rows in set (0.00 sec)

 

mysql> select * from employee;

+----+-------+------+

| id | name | did  |

+----+-------+------+

|  1| jack  |    1 |

|  2| marry |    1 |

+----+-------+------+

2 rows in set (0.00 sec)

--查詢軟件部的員工(利用子查詢)

mysql> select * from employee wheredid=(select id from department where name='軟件部');

+----+-------+------+

| id | name | did  |

+----+-------+------+

|  1| jack  |    1 |

|  2| marry |    1 |

+----+-------+------+

2 rows in set (0.05 sec)

--利用多表查詢

mysql> select e.name as 員工姓名,d.name  as 部門名稱 from employee e,department d where d.name='軟件部';

+--------------+--------------+

| 員工姓名     | 部門名稱     |

+--------------+--------------+

| jack         | 軟件部       |

| marry        | 軟件部       |

+--------------+--------------+

2 rows in set (0.01 sec)

============================多對多方案=============================

--建立的時候，先建立兩邊的，再建立中間的

--刪除的時候先刪除中間的，再刪除兩邊的

mysql> drop table if exists middle;

Query OK, 0 rows affected, 1 warning (0.00sec)

 

mysql> drop table if exists student;

Query OK, 0 rows affected (0.25 sec)

 

mysql> drop table if exists teacher;

Query OK, 0 rows affected (0.33 sec)

 

mysql> create table if not existsstudent(

   ->  id int primary keyauto_increment,

   ->  name varchar(20) not null

   -> );

Query OK, 0 rows affected (1.19 sec)

 

mysql> insert into student(name)values('jack');

Query OK, 1 row affected (0.08 sec)

 

mysql> insert into student(name)values('marry');

Query OK, 1 row affected (0.04 sec)

 

mysql> create table if not existsteacher(

    ->  id int primary key auto_increment,

   ->  name varchar(20) not null

   -> );

Query OK, 0 rows affected (1.43 sec)

 

mysql> insert into teacher(name)values('趙');

Query OK, 1 row affected (0.34 sec)

 

mysql> insert into teacher(name)values('蔡');

Query OK, 1 row affected (0.07 sec)

--多對多(外健放置在關聯表中，即將一個多對多拆分紅二個一對多關係)

-- 組合主鍵

mysql> create table if not existsmiddle(

   ->  sid int,

   ->  tid int,

   ->  constraint sid_FK foreignkey(sid) references student(id),

   ->  constraint tid_FK foreignkey(tid) references teacher(id),

   ->  primary key(sid,tid)

   -> );

Query OK, 0 rows affected (1.59 sec)

mysql> insert into middle(sid,tid)values(1,1);

Query OK, 1 row affected (0.14 sec)

 

mysql> insert into middle(sid,tid)values(1,2);

Query OK, 1 row affected (0.06 sec)

 

mysql> insert into middle(sid,tid)values(2,1);

Query OK, 1 row affected (1.07 sec)

mysql> insert into middle(sid,tid)values(2,2);

Query OK, 1 row affected (0.07sec)mysql> insert into middle(sid,tid) values(2,2);

--查詢趙教師教過的全部學員,組合查詢

--t.name='趙'  條件

-- and m.sid=s.id andm.tid=t.id  --錶鏈接起來

模式：

select 列出須要顯示的字段

from 列出所涉及到的全部表，建議寫別名

where 業務條件and 表關聯條件

--sql

mysql> selectt.name as 老師, s.name as 學員

    -> from teacher as t,student as s,middleas m

    -> where t.name = '趙'and m.sid=s.id and m.tid=t.id;

+--------+--------+

| 老師  | 學員   |

+--------+--------+

| 趙    | jack   |

| 趙    | marry  |

+--------+--------+

2 rows in set(0.00 sec)