表的完整性约束
二:not null与default
create table t1(
id int primary key auto_increment,
name varchar(16) not null,
sex enum('male','female') not null default 'male'
);
PRIMARY KEY (PK) 标识该字段为该表的主键，可以唯一的标识记录 唯一标识且不为空
FOREIGN KEY (FK) 标识该字段为该表的外键
NOT NULL 标识该字段不能为空
UNIQUE KEY (UK) 标识该字段的值是唯一的
AUTO_INCREMENT 标识该字段的值自动增长（整数类型，而且为主键）
DEFAULT 为该字段设置默认值
UNSIGNED 无符号
ZEROFILL 使用0填充
mysql> desc t1;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(16) | NO | | NULL | |
| sex | enum('male','female') | NO | | male | |
+-------+-----------------------+------+-----+---------+----------------+
不为空且没有设默认值，传值会报错
mysql> insert into t1(name) values('egon'),('lxx'),('alex');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select*from t1;
+----+------+------+
| id | name | sex |
+----+------+------+
| 1 | egon | male |
| 2 | lxx | male |
| 3 | alex | male |
+----+------+------+
三:unique key (索引)约束角度功能 约束指定的字段唯一，传入的值不能重复
egon命令行笔记
unique key
#针对单个字段的唯一
mysql> create database db2;
Query OK, 1 row affected (0.01 sec)
mysql> use db2;
Database changed
mysql> create table t1(
-> id int primary key auto_increment,
-> name varchar(16) not null,
-> sex enum('male','female') not null default 'male'
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> desc t1;
+-------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(16) | NO | | NULL | |
| sex | enum('male','female') | NO | | male | |
+-------+-----------------------+------+-----+---------+----------------+
3 rows in set (0.04 sec)
mysql> insert into t1(name) values('egon'),('lxx'),('alex');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select*from t1;
+----+------+------+
| id | name | sex |
+----+------+------+
| 1 | egon | male |
| 2 | lxx | male |
| 3 | alex | male |
+----+------+------+
3 rows in set (0.00 sec)
mysql> create table t2(x int unique);
Query OK, 0 rows affected (0.02 sec)
mysql> create table t3(
-> x int,
-> y varchar(5),
-> unique key(x)
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> desc t2;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| x | int(11) | YES | UNI | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.02 sec)
mysql> desc t3;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| x | int(11) | YES | UNI | NULL | |
| y | varchar(5) | YES | | NULL | |
+-------+------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> show create table t2;
+-------+-----------------------------------------------------------------------
----------------------------------------+
| Table | Create Table
|
+-------+-----------------------------------------------------------------------
----------------------------------------+
| t2 | CREATE TABLE `t2` (
`x` int(11) DEFAULT NULL,
UNIQUE KEY `x` (`x`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-----------------------------------------------------------------------
----------------------------------------+
1 row in set (0.00 sec)
mysql> show create table t3;
+-------+-----------------------------------------------------------------------
-----------------------------------------------------------------------+
| Table | Create Table
|
+-------+-----------------------------------------------------------------------
-----------------------------------------------------------------------+
| t3 | CREATE TABLE `t3` (
`x` int(11) DEFAULT NULL,
`y` varchar(5) DEFAULT NULL,
UNIQUE KEY `x` (`x`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-----------------------------------------------------------------------
-----------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> create table t4(
-> x int,
-> y varchar(5),
-> constraint uni_x unique key(x)
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> show create table t4;
+-------+-----------------------------------------------------------------------
---------------------------------------------------------------------------+
| Table | Create Table
|
+-------+-----------------------------------------------------------------------
---------------------------------------------------------------------------+
| t4 | CREATE TABLE `t4` (
`x` int(11) DEFAULT NULL,
`y` varchar(5) DEFAULT NULL,
UNIQUE KEY `uni_x` (`x`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-----------------------------------------------------------------------
---------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> desc t2;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| x | int(11) | YES | UNI | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)
mysql> insert into t2 values(null);
Query OK, 1 row affected (0.00 sec)
mysql> select*from t2;
+------+
| x |
+------+
| NULL |
+------+
1 row in set (0.00 sec)
mysql> select*from t2;
+------+
| x |
+------+
| NULL |
+------+
1 row in set (0.00 sec)
mysql> insert into t2 values(null);
Query OK, 1 row affected (0.00 sec)
mysql> select*from t2;
+------+
| x |
+------+
| NULL |
| NULL |
+------+
2 rows in set (0.00 sec)
mysql> insert into t2 values(1);
Query OK, 1 row affected (0.00 sec)
mysql> select*from t2;
+------+
| x |
+------+
| NULL |
| NULL |
| 1 |
+------+
3 rows in set (0.00 sec)
unique多列联合起来唯一
mysql> create table service(
-> ip varchar(15),
-> port int,
-> unique key(ip,port)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql> desc service;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| ip | varchar(15) | YES | MUL | NULL | |
| port | int(11) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.02 sec)
mysql> insert into service values('1.1.1.1',3306);
Query OK, 1 row affected (0.00 sec)
mysql> select*from service;
+---------+------+
| ip | port |
+---------+------+
| 1.1.1.1 | 3306 |
+---------+------+
1 row in set (0.00 sec)
mysql> insert into service values('1.1.1.1',3306);
ERROR 1062 (23000): Duplicate entry '1.1.1.1-3306' for key 'ip'
mysql> insert into service values('1.1.1.1',3356);
Query OK, 1 row affected (0.00 sec)
mysql> insert into service values('1.1.1.2',3306);
Query OK, 1 row affected (0.00 sec)
mysql> select*from service;
+---------+------+
| ip | port |
+---------+------+
| 1.1.1.1 | 3306 |
| 1.1.1.1 | 3356 |
| 1.1.1.2 | 3306 |
+---------+------+
3 rows in set (0.00 sec)
四 primary key
站在约束角度看primary key=not null unique 相当于结合体
以后但凡建表，必须注意：
1、必须有且只有一个主键
2、通常是id字段被设置为主键
create table t5(
id int primary key auto_increment,
);
mysql> desc t5;
+-------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
+-------+---------+------+-----+---------+----------------+
1 row in set (0.01 sec)
mysql> insert into t5 values(null);
Query OK, 1 row affected (0.00 sec)
mysql> select*from t5;
+----+
| id |
+----+
| 1 |
+----+
1 row in set (0.00 sec)
mysql> create table t6(x int primary key);
Query OK, 0 rows affected (0.02 sec)
mysql> desc t6;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| x | int(11) | NO | PRI | NULL | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.03 sec)
mysql> insert into t6 values(null);
ERROR 1048 (23000): Column 'x' cannot be null
mysql> insert into t6 values(1);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t6 values(1);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'
mysql> select*from t6;
+---+
| x |
+---+
| 1 |
+---+
1 row in set (0.00 sec)
#不能指定多个主键的情况
mysql> create table t7(x int primary key,y int primary key);
ERROR 1068 (42000): Multiple primary key defined
#未指定主键默认自定义主键
mysql> create table t7(x int,y varchar(5),z int not null unique);
Query OK, 0 rows affected (0.02 sec)
mysql> desc t7;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| x | int(11) | YES | | NULL | |
| y | varchar(5) | YES | | NULL | |
| z | int(11) | NO | PRI | NULL | |
+-------+------------+------+-----+---------+-------+
只要是innodb存储引擎一定会要主键
mysql> create table t8(x int,y varchar(5),z int);
Query OK, 0 rows affected (0.03 sec)
mysql> create table t9(x int,y varchar(5),z int not null unique,m int not null u
nique);
Query OK, 0 rows affected (0.22 sec)
mysql> desc t9;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| x | int(11) | YES | | NULL | |
| y | varchar(5) | YES | | NULL | |
| z | int(11) | NO | PRI | NULL | |
| m | int(11) | NO | UNI | NULL | |
+-------+------------+------+-----+---------+-------+
4 rows in set (0.03 sec)
表的存储引擎
自己处理自己的数据用不同的文件来处理，文件分不同的类型，表也分不同的类型
表的类型有一个专有的名词，称之为存储引擎，为一个表指定了存储引擎，相当于创建了表的类型
transaction交易
rowlevel行级锁
四:primary key(索引)约束角度的功能
站在约束角度看primary key=not null unique
index key(索引)
目的是为了加速查询用的，不常用
五:foreign key
存储引擎
create table t12(x int)engine='myisam'; create table t13(x int)engine='innodb'; create table t14(x int)engine='memory'; create table t15(x int)engine='blackhole'; frm存表的结构 myd代表的是myisam存储引擎的数据文件 myi代表的是index的意思存放的是索引 ibd代表的是又存数据又存索引 客户端不存数据，存的是服务端
外键
表之间的关系
表其他相关操作