https://blog.csdn.net/u012750578/article/details/15026677
Mysql表的約束設計和關聯關系設計
======================表的完整性======================
(1)實體完整性：每條記錄有一個唯一標識符，通常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一定的規則
定義主鍵約束
primary key:不允許為空，不允許重復
刪除主鍵：alter table tablename drop primary key ;
定義主鍵自動增長(id,沒有業務含義)
auto_increment(MySQL特有/UUID類生成)
定義唯一約束
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：只有唯一字段
(2)組合主鍵：由多個字段組合起來，形成唯一字段
(3)外鍵：針對多張表之間的關聯
3 主鍵的特點
(1)主鍵不能重復
(2)主鍵不能為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，通常使用UUID來生成唯一的主鍵值，便於多個合並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)
--主鍵不能重復,主鍵沖突,1代表第一列，即id列
mysql> insert into teachervalues(1,'marry','1996-2-12');
ERROR 1062 (23000): Duplicate entry '1' forkey 'PRIMARY'
mysql>
--主鍵不能為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，要么是一列，要么是多列
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自動增長
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增長的序列
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，通常使用UUID來生成唯一的主鍵值，便於多個合並數據時依然保持實體完整性
4 唯一約束的特點
(1)非NULL值不能重復
(2)可以插入多個NULL值
(3)'NULL'空串和NULL是不同的概念
mysql> drop table teacher;
Query OK, 0 rows affected (0.42 sec)
--唯一
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)
--違反唯一
mysql> insert intoteacher(name,birthday) values('marry','2011-2-2');
ERROR 1062 (23000): Duplicate entry 'marry'for key 'name'
5 非空約束特點
(1)不能插入NULL值
(2)主鍵約束=非NULL約束+唯一約束
--違返不為空約束
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 外健特點
(1)外鍵值必須來源於所引用別一個表主鍵值，或NULL
*7 關聯關系
(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成二個一對多關系)
一對一關系一:
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為外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可以插入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為3的出錯誤，外鍵pid必須來源另一表的主鍵值或為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
--有外鍵關系的行不能刪除，需先刪除其關聯的外鍵關系,再進行刪除主鍵關系的數據，與創建的時候相反
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`))
一對一關系方式二:主鍵當作另一個表的外鍵
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)
--使用主鍵作為外鍵
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為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，因為這里id為一個非空的屬性
mysql> insert into card(location)values(NULL);
ERROR 1048 (23000): Column 'location'cannot be null
==========================一對多關系=============================
設計方案:
一方做一個容器，多方做一個引用
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=============================
--創建的時候，先創建兩邊的，再創建中間的
--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成二個一對多關系)
-- 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);
--查詢趙教師教過的所有學員,組合查詢
--t.name='趙' 條件
-- and m.sid=s.id andm.tid=t.id --表連接起來
模式：
select 列出需要顯示的字段
from 列出所涉及到的所有表，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)