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创建数据表主键外键
1、创建数据表
按行和列的方式存储，每一行唯一一条记录，每一列代表记录中的某个字段或者是域。
格式：表的名称不区分大小写，不能使用SQL关键字；存在多列使用逗号分隔。
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create table
(
字段1，数据类型 [列约束条件]，
字段2，数据类型 [列约束条件]，
字段3，数据类型 [列约束条件]，
........
[表级别约束条件]
); 测试：表名test01
| 字段名 | 数据类型 |
| name | varchar (30) |
| id | int (11) |
（1）主键约束
单字段
MySQL> create table test02
-> (id int(11) primary key,
-> name varchar(30));
Query OK, 0 rows affected (0.08 sec)mysql> create table test03
-> (id int(11),
-> name varchar(30),
-> primary key (id));
Query OK, 0 rows affected (0.10 sec)mysql> desc test02;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(30) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> desc test03;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | 0 | |
| name | varchar(30) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
列的会隐含一个rowid字段
表的会明确要求id是可识别的标志
多字段
mysql> create table test05 (id int(11), name varchar(30),primary key(id,name));
Query OK, 0 rows affected (0.11 sec)
删除主键约束
mysql> alter table test0004 drop primary key; Query OK, 0 rows affected (0.08 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table test0004\G;
*************************** 1. row *************************** Table: test0004
Create Table: CREATE TABLE 'test0004` ( `username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL DEFAULT '0',
`age` tinyint(3) unsigned NOT NULL,
UNIQUE KEY `username` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 1 row in set (0.00 sec) mysql> desc test0004;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+ |
username | varchar(10) | NO | PRI | NULL | | |
pid | smallint(5) unsigned | YES | | NULL | | |
id | smallint(5) unsigned | NO | | 0 | | |
age | tinyint(3) unsigned | NO | | NULL |
| +----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)怎么在已有的表中添加主键呢？
举个例子：
创建一个书记表，后在增加一个字段
mysql> create table test0004( username varchar(10) not null, pid smallint unsigned);
Query OK, 0 rows affected (0.13 sec)
mysql> desc test0004;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | | NULL | |
| pid | smallint(5) unsigned | YES | | NULL | |
+----------+----------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> alter table test0004 add id smallint unsigned;
Query OK, 0 rows affected (0.10 sec)
Records: 0 Duplicates: 0 Warnings: 0增加一个主键然后验证
mysql> alter table test0004 add constraint PK_test0004_id primary key (id);
Query OK, 0 rows affected (0.10 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test0004;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | | NULL | |
| pid | smallint(5) unsigned | YES | | NULL | |
| id | smallint(5) unsigned | NO | PRI | 0 | |
+----------+----------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> show create table test0004\G;
*************************** 1. row ***************************
Table: test0004
Create Table: CREATE TABLE `test0004` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)那我们添加一个唯一约束来看一下
mysql> alter table test0004 add unique (username);
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table test0004\G;
*************************** 1. row ***************************
Table: test0004
Create Table: CREATE TABLE `test0004` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`id`),
UNIQUE KEY `username` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)接下来我们给他添加一个字段，并修改和删除默认值操作
mysql> alter table test0004 add age tinyint unsigned not null;
Query OK, 0 rows affected (0.13 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test0004;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | UNI | NULL | |
| pid | smallint(5) unsigned | YES | | NULL | |
| id | smallint(5) unsigned | NO | PRI | 0 | |
| age | tinyint(3) unsigned | NO | | NULL | |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> alter table test0004 alter age set default 15;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test0004;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | UNI | NULL | |
| pid | smallint(5) unsigned | YES | | NULL | |
| id | smallint(5) unsigned | NO | PRI | 0 | |
| age | tinyint(3) unsigned | NO | | 15 | |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
mysql> alter table test0004 alter age drop default;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0（2）外键束缚
一个表可以有一个或多个外键；保证数据的一致性完整性；定义外键之后，不
允许删除另一个表中具有关联关系的记录。
主表：对于两个表具有关联关系的，具有主键的表；
从表：对于两个表具有关联关系的，具有外键的表；
constraint <外建名> foreign key<字段名> references <主表名> 主键列
mysql> create table test06
-> (id int(11) primary key,
-> name varchar(30) not null);
Query OK, 0 rows affected (0.16 sec)mysql> create table test07 (id int(11) primary key, name varchar(30), constraint test0607 foreign key(id) references test06(id) );
Query OK, 0 rows affected (0.19 sec)
加深：
首先创一个provin1表
mysql> create table provin1( id smallint unsigned primary key auto_increment, pnaame varchar(20) not null );
Query OK, 0 rows affected (0.09 sec)
mysql> show create table provin1\G;
*************************** 1. row ***************************
Table: provin1
Create Table: CREATE TABLE `provin1` (
`id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`pname` varchar(20) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)再创建一个test0003的表
mysql> create table test0003( id smallint unsigned primary key auto_increment, ussername varchar(10) not null, pid smallint unsigned, foreign key (pid) referencess provin1 (id) on delete cascade);
Query OK, 0 rows affected (0.08 sec)
mysql> show create table test0003\G;
*************************** 1. row ***************************
Table: test0003
Create Table: CREATE TABLE `test0003` (
`id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `pid` (`pid`),
CONSTRAINT `test0003_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `provin1` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.01 sec)向provin1中插入数据
mysql> insert provin1 (pname) values ('A');
Query OK, 1 row affected (0.00 sec)
mysql> insert provin1 (pname) values ('b');
Query OK, 1 row affected (0.00 sec)
mysql> insert provin1 (pname) values ('C');
Query OK, 1 row affected (0.00 sec)
mysql> select * from provin1;
+----+-------+
| id | pname |
+----+-------+
| 1 | A |
| 3 | b |
| 5 | C |
+----+-------+
3 rows in set (0.00 sec)向test0003中插入数据
mysql> insert test0003(username,pid) values ('tom',3);
Query OK, 1 row affected (0.00 sec)
mysql> insert test0003(username,pid) values ('lichao',5);
Query OK, 1 row affected (0.00 sec)
mysql> insert test0003(username,pid) values ('chenchen',1);
Query OK, 1 row affected (0.00 sec)
mysql> insert test0003(username,pid) values ('cat',3);
Query OK, 1 row affected (0.00 sec)
mysql> insert test0003(username,pid) values ('nihao',7);
ERROR 1452 (23000): Cannot add or update a child row:
a foreign key constraint fails (`chenchen`.`test0003`, CONSTRAINT
`test0003_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `provin1`
(`id`) ON DELETE CASCADE)我们看到插入pid =7的时候出错了，错误原因是因为pid所对应provin1表中没有7这个id，所以他会报错，我们来看看test0003表中数据
mysql> select * from test0003;
+----+----------+------+
| id | username | pid |
+----+----------+------+
| 1 | tom | 3 |
| 3 | lichao | 5 |
| 5 | chenchen | 1 |
| 7 | cat | 3 |
+----+----------+------+
4 rows in set (0.01 sec)那么我们来去除一下provin1里边的id为3的字段来查看test0003表中的变化
mysql> delete from provin1 where id = 3;
Query OK, 1 row affected (0.00 sec)
mysql> select * from provin1;
+----+-------+
| id | pname |
+----+-------+
| 1 | A |
| 5 | C |
+----+-------+
2 rows in set (0.00 sec)
mysql> select * from test0003;
+----+----------+------+
| id | username | pid |
+----+----------+------+
| 3 | lichao | 5 |
| 5 | chenchen | 1 |
+----+----------+------+
2 rows in set (0.00 sec)我们看到去除provin1中的id为3的数据后test0003表中对应的pid为3的字段消失，此验证了外键束缚中的 cascade功能。
cascade：从父表删除或更新且自动删除或跟新子表中匹配的行.
下边我会整理其他约束和mysql表操作文档，陆续更新中，本文禁止转载，个人总结不易，请谅解
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