从今天开始学习mysql数据库，希望以后能够记录自己学习的点点滴滴
mysql中创建数据表
1.创建一个数据库为test_db
mysql> create database test_db;
Query OK, 1 row affected (0.00 sec)
切换到test_db上
mysql> use test_db;
Database changed
mysql>
2.创建一个表tb_emp1
create table tb_emp1
(
id INT(11),
name VARCHAR(25),
deptid INT (11),
salary FLOAT
);
mysql> create table tb_emp1
-> (
-> id INT(11),
-> name VARCHAR(25),
-> deptid INT (11),
-> salary FLOAT
-> );
Query OK, 0 rows affected (0.09 sec)
mysql> show tables;
+-------------------+
| Tables_in_test_db |
+-------------------+
| tb_emp1 |
+-------------------+
1 row in set (0.01 sec)
mysql> show create table tb_emp1 \G;
*************************** 1. row ***************************
Table: tb_emp1
Create Table: CREATE TABLE `tb_emp1` (
`id` int(11) DEFAULT NULL,
`name` varchar(25) DEFAULT NULL,
`deptid` int(11) DEFAULT NULL,
`salary` float DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
mysql>
3.使用主键约束
语法是字段名数据类型 primary key [默认值]
create table tb_emp2
(
id INT(11) PRIMARY KEY,
name VARCHAR(25),
deptid INT (11),
salary FLOAT
);
或者如下
create table tb_emp2
(
id INT(11) ,
name VARCHAR(25),
deptid INT (11),
salary FLOAT
PRIMARY KEY (id)
);
mysql> create table tb_emp2
-> (
-> id INT(11) PRIMARY KEY,
-> name VARCHAR(25),
-> deptid INT (11),
-> salary FLOAT
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> show tables;
+-------------------+
| Tables_in_test_db |
+-------------------+
| tb_emp1 |
| tb_emp2 |
+-------------------+
2 rows in set (0.00 sec)
mysql> show create table tb_emp2 \G;
*************************** 1. row ***************************
Table: tb_emp2
Create Table: CREATE TABLE `tb_emp2` (
`id` int(11) NOT NULL,
`name` varchar(25) DEFAULT NULL,
`deptid` int(11) DEFAULT NULL,
`salary` float DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
mysql>
4.表中使用外键
语法[constraint <外键名>] foreign key字段名1 [,字段名2,…] references <主表名>
主键列1[,主键列2,…]
主表：
create table tb_dept
(
deptid int(11) primary key,
name varchar(22) not null,
location varchar(50)
)
从表：
create table tb_emp3
(
id int(11) primary key,
name varchar(25),
location varchar(50),
deptid int(11),
salary float,
constraint fk_emp_dept foreign key (deptid) references tb_dept (deptid)
);
mysql> create table tb_dept
-> (
-> deptid int(11) primary key,
-> name varchar(22) not null,
-> location varchar(50)
-> )
-> ;
Query OK, 0 rows affected (0.05 sec)
mysql> create table tb_emp3
-> (
-> id int(11) primary key,
-> name varchar(25),
-> location varchar(50),
-> deptid int(11),
-> salary float,
-> constraint fk_emp_dept foreign key (deptid) references tb_dept (deptid)
-> );
Query OK, 0 rows affected (0.06 sec)
mysql>
mysql> show tables;
+-------------------+
| Tables_in_test_db |
+-------------------+
| tb_dept |
| tb_emp1 |
| tb_emp2 |
| tb_emp3 |
+-------------------+
4 rows in set (0.00 sec)
mysql> show create table tb_emp3 \G;
*************************** 1. row ***************************
Table: tb_emp3
Create Table: CREATE TABLE `tb_emp3` (
`id` int(11) NOT NULL,
`name` varchar(25) DEFAULT NULL,
`location` varchar(50) DEFAULT NULL,
`deptid` int(11) DEFAULT NULL,
`salary` float DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_emp_dept` (`deptid`),
CONSTRAINT `fk_emp_dept` FOREIGN KEY (`deptid`) REFERENCES `tb_dept` (`deptid`
)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
mysql>
5.表空使用非空约束(not null )和唯一约束(unique)
语法字段名数据类型 not null ,字段名数据类型 unique
create table tb_dept1
(
deptid int(11) primary key,
name varchar(22) unique,
location varchar(50) not null
);
mysql> create table tb_dept1
-> (
-> deptid int(11) primary key,
-> name varchar(22) unique,
-> location varchar(50) not null
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> show create table tb_dept1 \G;
*************************** 1. row ***************************
Table: tb_dept1
Create Table: CREATE TABLE `tb_dept1` (
`deptid` int(11) NOT NULL,
`name` varchar(22) DEFAULT NULL,
`location` varchar(50) NOT NULL,
PRIMARY KEY (`deptid`),
UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
6.使用默认值
语法字段名数据库类型 default
mysql> create table tb_emp4
-> (
-> id int(11) primary key,
-> name varchar(25),
-> location varchar(50),
-> deptid int(11) default 1111,
-> salary float
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> show create table tb_emp4 \G;
*************************** 1. row ***************************
Table: tb_emp4
Create Table: CREATE TABLE `tb_emp4` (
`id` int(11) NOT NULL,
`name` varchar(25) DEFAULT NULL,
`location` varchar(50) DEFAULT NULL,
`deptid` int(11) DEFAULT '1111',
`salary` float DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
mysql>
7.设置表的属性字段增加（auto_increment）
mysql> create table tb_emp5
-> (
-> id int(11) primary key auto_increment,
-> name varchar(25),
-> location varchar(50),
-> deptid int(11) default 1111,
-> salary float
-> );
Query OK, 0 rows affected (0.13 sec)
mysql> show tables ;
+-------------------+
| Tables_in_test_db |
+-------------------+
| tb_dept |
| tb_dept1 |
| tb_emp1 |
| tb_emp2 |
| tb_emp3 |
| tb_emp4 |
| tb_emp5 |
+-------------------+
7 rows in set (0.00 sec)
mysql> desc tb_emp5;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL |auto_increment |
| name | varchar(25) | YES | | NULL | |
| location | varchar(50) | YES | | NULL | |
| deptid | int(11) | YES | | 1111 | |
| salary | float | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> show create table tb_emp5 \G;
*************************** 1. row ***************************
Table: tb_emp5
Create Table: CREATE TABLE `tb_emp5` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(25) DEFAULT NULL,
`location` varchar(50) DEFAULT NULL,
`deptid` int(11) DEFAULT '1111',
`salary` float DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
mysql>
插入如下语句验证；
mysql> insert into tb_emp5 (name,location,salary) values('ww','dd','1000'),('ja
ck','ds','3000'),('rrw','dd','1500');
Query OK, 3 rows affected (0.03 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from tb_emp5;
+----+------+----------+--------+--------+
| id | name | location | deptid | salary |
+----+------+----------+--------+--------+
| 1 | ww | dd | 1111 | 1000 |
| 2 | jack | ds | 1111 | 3000 |
| 3 | rrw | dd | 1111 | 1500 |
+----+------+----------+--------+--------+
3 rows in set (0.00 sec)
mysql>