数据库管理及数据类型

<h1><center>数据库管理及数据类型</center></h1>

**作者：行癫（盗版必究）**

------

## 一：数据类型

#### 1.数值类型

##### 整数类型

​		整数类型：TINYINT SMALLINT MEDIUMINT INT BIGINT

​		作用：用于存储用户的年龄、游戏的Level、经验值等

![image-20220920124821420](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920124821420.png)

##### 浮点数类型

​		浮点数类型：FLOAT DOUBLE

​		作用：用于存储用户的身高、体重、薪水等

![image-20220920124919373](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920124919373.png)

```shell
float(5,3)      5宽度  3精度
注意：
	宽度不算小数点
	宽度-精度=点前
案例：
MySQL [(none)]> create database diandian;
Query OK, 1 row affected (0.00 sec)

MySQL [(none)]> use diandian
Database changed
MySQL [diandian]> create table t1(id float(6,2));
Query OK, 0 rows affected (0.24 sec)

MySQL [diandian]> insert into t1 values('2.22');
```

##### 定点数类型

​		定点数类型：DEC

​		定点数在MySQL内部以字符串形式存储，比浮点数更精确，适合用来表示货币等精度高的数据

##### 位类型

​		位类型：BIT

​		BIT(M)可以用来存放多位二进制数，M范围从1~64，如果不写默认为1位

#### 2.字符串类型

​		CHAR系列  	CHAR  VARCHAR

​		TEXT系列   	TINYTEXT TEXT MEDIUMTEXT LONGTEXT

​		BLOB 系列	    TINYBLOB BLOB MEDIUMBLOB LONGBLOB 

​		BINARY系列 	BINARY VARBINARY 

![image-20220920132114919](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920132114919.png)

##### 枚举类型

​		枚举类型：枚举列可以把一些不重复的字符串存储成一个预定义的集合		

```shell
mysql> create table enum_table( e ENUM('fish','apple','dog'));
Query OK, 0 rows affected (0.35 sec)        
mysql> insert into enum_table(e) values('fish');
Query OK, 1 row affected (0.11 sec)

mysql> select * from enum_table;
+------+
| e    |
+------+
| fish |
+------+
1 row in set (0.00 sec)

mysql> insert into enum_table(e) values('nihao');
ERROR 1265 (01000): Data truncated for column 'e' at row 1
```

##### 时间和日期类型

​		时间和日期类型：DATE TIME DATETIME TIMESTAMP YEAR 

​		作用：用于存储用户的注册时间，文章的发布时间，文章的更新时间，员工的入职时间等

![image-20220920132630856](https://xingdian-image.oss-cn-beijing.aliyuncs.com/xingdian-image/image-20220920132630856.png)

```shell
mysql> create table t8 (
  id1 timestamp NOT NULL default CURRENT_TIMESTAMP,
  id2  datetime default NULL
);

        timestamp 类型的列还有个特性：默认情况下，在 insert, update 数据时，timestamp 列会自动以当前时间（CURRENT_TIMESTAMP）填充/更新。“自动”的意思就是，你不去管它，MySQL 会替你去处理。
                
mysql> insert into t8(id1) values('20180109000000');        
mysql> select * from t8;
+---------------------+------+
| id1                 | d2   |
+---------------------+------+
| 2018-01-09 00:00:00 | NULL |
+---------------------+------+
1 row in set (0.00 sec)

扩展： 
select now();查看当前时间
```

## 二：表操作

#### 1.案例

表:：school.student1

```
字段		    字段		        字段
id             name	        sex		       age
1              tom		    male	        23		 记录
2              jack		    male	        21		 记录
3              alice	    female	        19		  记录
```

语法：

```shell
create table 表名(自定义)(
		字段名1  类型[(宽度) 约束条件],
		字段名2  类型[(宽度) 约束条件],
		字段名3  类型[(宽度) 约束条件]
)[存储引擎 字符集];
==在同一张表中，字段名是不能相同
==宽度和约束条件可选
==字段名和类型是必须的
```

创建库表：

```shell
mysql> CREATE  DATABASE school;				        //创建数据库school
mysql> use school;
mysql> create table student1(
    id int,
    name varchar(50),                 
    sex enum('m','f'),
    age int
     );
Query OK, 0 rows affected (0.03 sec)
```

查看库：

```shell
mysql> show tables;			                                    
+------------------+
| Tables_in_school |
+------------------+
| student1         |
+------------------+
1 row in set (0.00 sec)
```

插入语法：

```
insert into 表名(字段1,字段2...)  values(字段值列表...);
```

插入数据：

```shell
mysql> insert into student1(id,name,sex,age) values(1,'xingdia','m','26');
```

查看表结构：

```shell
mysql> desc student1;
+-------+---------------+------+-----+---------+-------+
| Field | Type          | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| id    | int(11)       | YES  |     | NULL    |       |
| name  | varchar(50)   | YES  |     | NULL    |       |
| sex   | enum('m','f') | YES  |     | NULL    |       |
| age   | int(11)       | YES  |     | NULL    |       |
+-------+---------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
```

查询数据：

```shell
mysql> select id,name,sex,age from student1;	//查询表中所有字段的值
Empty set (0.00 sec)

mysql> select * from student1;		/查询表中所有字段的值
Empty set (0.00 sec)

mysql> select name,age from student1;		      //查询表中指定字段的值
Empty set (0.00 sec)
```

扩展插入：

```shell
mysql> insert into student1 values (1,'xingdian','m',33),(2,'alice','m',20),(3,'jack','m',40);          //顺序插入
Query OK, 3 rows affected (0.14 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> insert into student1(name,age) values ('zhuzhu',10),('gougou',20);          //只向指定的字段插入值
Query OK, 2 rows affected (0.12 sec)
Records: 2  Duplicates: 0  Warnings: 0
```

#### 2.案例

表：school.student2

```shell
               字段名             数据类型
编号             id                   int
姓名			  name			      varchar(50)
出生年份	     born_year	          year
生日			  birthday		      date
上课时间	     class_time	         time
注册时间	     reg_time		     datetime
```

创建表：

```shell
mysql> create table student2(
    id int,
    name varchar(50),         
    born_year year,
    birthday date,
    class_time time,
    reg_time datetime 
    );
```

插入数据：

```shell
mysql> insert into student2 values(1,'tom',now(),now(),now(),now());
mysql> insert into student2 values(2,'jack',1982,19821120,123000,20140415162545);
```

表：school.student3

```shell
id     id              int
姓名	name	    varchar(50)
性别	sex		    enum('male','female')
爱好	hobby	    set('music','book','game','disc')
```

创建表：

```shell
mysql> create table student3(
     id int,
     name varchar(50),
     sex enum('male','female'),
     hobby set('music','book','game','disc')
     );
```

查看表结构：

```shell
mysql> desc student3;
mysql> show create table student3\G
```

插入数据：

```shell
mysql> insert into student3 values (1,'tom','male','book,game');
mysql> insert into student3 values (2,'jack','male','film');
```

注意：

​		DESCRIBE查看表结构

```shell
DESCRIBE 表名;
DESC 表名;
```

​		查看表详细结构

```shell
SHOW CREATE TABLE 表名;
```

## 三：表完整性约束

#### 1.作用

​		用于保证数据的完整性和一致性

#### 2.约束条件

PRIMARY KEY (PK)		标识该字段为该表的主键，可以唯一的标识记录，不可以为空  UNIQUE + NOT NULL

FOREIGN KEY (FK)		 标识该字段为该表的外键，实现表与表（父表主键/子表1外键/子表2外键）之间的关联

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，可以为空，一个表中可以有多个UNIQUE KEY

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

注意：

​		是否允许为空，默认NULL，可设置NOT NULL，字段不允许为空，必须赋值

​		字段是否有默认值，缺省的默认值是NULL，如果插入记录时不给字段赋值，此字段使用默认值

```shell
MySQL [(none)]> sex enum('male','female') not null default 'male'
MySQL [(none)]> age int unsigned NOT NULL default 20 		必须为正值（无符号） 不允许为空  默认是20
```

​		是否是key		主键 primary key		外键 forengn key

#### 3.NOT NULL

表：school.student4

创建表：（注意前提需要有库）

```shell
mysql> create table school.student4(
    id int not null,
    name varchar(50) not null,
    sex enum('m','f') default 'm' not null,
    age int unsigned default 18 not null,
    hobby set('music','disc','dance','book') default 'book,dance'
   );
```

插入数据：（注意观察查询到的数据）

```shell
MySQL [(none)]> insert into school.student4(id,name) values(2,'robin');
Query OK, 1 row affected (0.08 sec)

MySQL [(none)]> select * from school.student4;
+----+-------+-----+-----+------------+
| id | name  | sex | age | hobby      |
+----+-------+-----+-----+------------+
|  2 | robin | m   |  18 | dance,book |
+----+-------+-----+-----+------------+
1 row in set (0.00 sec)
```

注意报错的原因：

```shell
MySQL [(none)]> insert into school.student4 values(3,NULL,'m',40,'book');
ERROR 1048 (23000): Column 'name' cannot be null
```

#### 4.唯一约束

作用：

​		MySQL索引的建立对于MySQL的高效运行是很重要的，索引可以大大提高MySQL的检索速度

表：company.department1

创建表：

```shell
MySQL [(none)]> create database company;
Query OK, 1 row affected (0.01 sec)
MySQL [(none)]> CREATE TABLE company.department1 (dept_id INT,dept_name VARCHAR(30) UNIQUE,comment VARCHAR(50));
Query OK, 0 rows affected (0.34 sec)
```

查看表结构：

```shell
MySQL [(none)]> desc company.department1;
+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| dept_id   | int(11)     | YES  |     | NULL    |       |
| dept_name | varchar(30) | YES  | UNI | NULL    |       |
| comment   | varchar(50) | YES  |     | NULL    |       |
+-----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
```

数据插入：（注意查看插入数据时的提示）

```shell
MySQL [(none)]> insert into company.department1 values ("1","xingdian","hr");
Query OK, 1 row affected (0.04 sec)

MySQL [(none)]> insert into company.department1 values ("1","xingdian","hr");
ERROR 1062 (23000): Duplicate entry 'xingdian' for key 'dept_name'
```

#### 5.主键约束

注意：primary key 字段的值是不允许重复，且不允许不NULL（UNIQUE + NOT NULL）

表：school.student6

创建表：

```shell
MySQL [(none)]> create table school.student6(
    ->     id int primary key not null auto_increment,
    ->     name varchar(50) not null,
    ->     sex enum('male','female') not null default 'male', 
    ->     age int not null default 18
    ->     );
Query OK, 0 rows affected (0.47 sec)
```

插入数据：

```shell
MySQL [(none)]> insert into school.student6 values (1,'alice','female',22);
Query OK, 1 row affected (0.18 sec)

MySQL [(none)]> insert into school.student6(name,sex,age) values
    ->      ('jack','male',19),
    ->      ('tom','male',23);
Query OK, 2 rows affected (0.14 sec)
Records: 2  Duplicates: 0  Warnings: 0

MySQL [(none)]> select * from school.student6;
+----+-------+--------+-----+
| id | name  | sex    | age |
+----+-------+--------+-----+
|  1 | alice | female |  22 |
|  2 | jack  | male   |  19 |
|  3 | tom   | male   |  23 |
+----+-------+--------+-----+
3 rows in set (0.00 sec)

```

## 四：修改表

语法格式：

修改表名

​	  ALTER TABLE 表名  RENAME 新表名;

增加字段

​	  ALTER TABLE 表名

​                    	  ADD 字段名  数据类型 [完整性约束条件…],

​                          ADD 字段名  数据类型 [完整性约束条件…];

​    ALTER TABLE 表名

​	                  	  ADD 字段名  数据类型 [完整性约束条件…]  AFTER 字段名;
删除字段

​	ALTER TABLE 表名 DROP 字段名;

修改字段

​	  ALTER TABLE 表名  MODIFY 字段名 数据类型 [完整性约束条件…];

​	  ALTER TABLE 表名  CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…];

​	  ALTER TABLE 表名  CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];

#### 1.修改数据库引擎

```shell
mysql> alter table service engine=innodb;     //engine=myisam|memory|....
```

#### 2.添加字段

```shell
mysql> create table student10 (id int);
mysql> alter table student10 add name varchar(20) not null, add age int not null default 22;

mysql> alter table student10 add stu_num int not null after name;   //添加name字段之后

mysql> alter table student10 add sex enum('male','female') default 'male' first;  //添加到最前面
```

#### 3.删除字段

```shell
mysql> alter table student10 drop sex;
```

#### 4.修改字段类型

```shell
MySQL [school]> desc student10;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | YES  |     | NULL    |       |
| age   | int(11) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.01 sec)

MySQL [school]>  alter table student10 modify age tinyint  not null ;  
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student10;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(11)    | YES  |     | NULL    |       |
| age   | tinyint(4) | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+
2 rows in set (0.00 sec)  

MySQL [school]> alter table student10 modify id int not null primary key ;  ////修改字段类型、约束、主键
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student10;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(11)    | NO   | PRI | NULL    |       |
| age   | tinyint(4) | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+
```

#### 5.增加约束

```shell
MySQL [school]> alter table student10 modify id int not null primary key ;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student10;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(11)    | NO   | PRI | NULL    |       |
| age   | tinyint(4) | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

MySQL [school]> alter table student10 modify id int not null primary key auto_increment; 
ERROR 1068 (42000): Multiple primary key defined   //错误，该字段已经是primary key

MySQL [school]> alter table student10 modify id int not null auto_increment;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student10;
+-------+------------+------+-----+---------+----------------+
| Field | Type       | Null | Key | Default | Extra          |
+-------+------------+------+-----+---------+----------------+
| id    | int(11)    | NO   | PRI | NULL    | auto_increment |
| age   | tinyint(4) | NO   |     | NULL    |                |
+-------+------------+------+-----+---------+----------------+
```

#### 6.增加主键

```shell
MySQL [school]> desc student1;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | YES  |     | NULL    |       |
| age   | int(11) | YES  |     | NULL    |       |
| name  | char(1) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)

MySQL [school]> alter table student1 add primary key(id);

MySQL [school]> desc student1;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | NO   | PRI | NULL    |       |
| age   | int(11) | YES  |     | NULL    |       |
| name  | char(1) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
3 rows in set (0.00 sec)
```

#### 7.修改主键和自增

```shell
MySQL [school]> alter table student1 modify id int  auto_increment;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student1;
+-------+---------+------+-----+---------+----------------+
| Field | Type    | Null | Key | Default | Extra          |
+-------+---------+------+-----+---------+----------------+
| id    | int(11) | NO   | PRI | NULL    | auto_increment |
| age   | int(11) | YES  |     | NULL    |                |
| name  | char(1) | YES  |     | NULL    |                |
+-------+---------+------+-----+---------+----------------+
```

#### 8.删除主键

```shell
MySQL [school]> desc student10;
+-------+------------+------+-----+---------+----------------+
| Field | Type       | Null | Key | Default | Extra          |
+-------+------------+------+-----+---------+----------------+
| id    | int(11)    | NO   | PRI | NULL    | auto_increment |
| age   | tinyint(4) | NO   |     | NULL    |                |
+-------+------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

MySQL [school]> alter table student10 drop primary key;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

删除自增
ySQL [school]>  alter table student10 modify id int not null;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student10;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(11)    | NO   | PRI | NULL    |       |
| age   | tinyint(4) | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+

MySQL [school]> alter table student10 drop primary key;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

MySQL [school]> desc student10;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(11)    | NO   |     | NULL    |       |
| age   | tinyint(4) | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
```

#### 9.复制表

复制表结构＋记录 （key不会复制: 主键、外键和索引）复制表结构/记录+表结构，不会将Key复制

```shell
mysql> create table new_service select * from service;
```

只复制表结构

```shell
mysql> create table new1_service select * from service where 1=2;   //条件为假，查不到任何记录
```

可以复制主键,只复制表结构

```shell
mysql> create table t4 like employees;
```

#### 10.删除表

```shell
mysql> DROP TABLE 表名;
```

#### 11.修改数据表中字段的值

语法：

​		Update 表名 set 列名=值where 条件

```shell
mysql> update student set name='123' where id=1;
```

删除某一行：

​		delete from 表名 where id=1

```shell
mysql> delete from type where id=1;
```

## 五：库操作

#### 1.简介

​		系统自带库的含义及作用

```shell
MySQL [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
```

information_schema：虚拟库，主要存储了系统中的一些数据库对象的信息，例如用户表信息、列信息、权限信息、字符信息等

performance_schema：主要存储数据库服务器的性能参数

mysql：授权库，主要存储系统用户的权限信息

sys：主要存储数据库服务器的性能参数

注意：information_schema

​		SCHEMATA     存放的是系统中的库

```shell
MySQL [information_schema]> select * from information_schema.SCHEMATA;
+--------------+--------------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME        | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+--------------------+----------------------------+------------------------+----------+
| def          | information_schema | utf8                       | utf8_general_ci        | NULL     |
| def          | mysql              | latin1                     | latin1_swedish_ci      | NULL     |
| def          | performance_schema | utf8                       | utf8_general_ci        | NULL     |
| def          | school             | latin1                     | latin1_swedish_ci      | NULL     |
| def          | sys                | utf8                       | utf8_general_ci        | NULL     |
+--------------+--------------------+----------------------------+------------------------+----------+

目录_名称
实际库_名称
默认_字符_设置_名称
默认_分类_名称
```

​		TABLES   存储表名

```shell
MySQL [information_schema]> select * from information_schema.TABLES\G
*************************** 283. row ***************************
  TABLE_CATALOG: def
   TABLE_SCHEMA: xingdian
     TABLE_NAME: t1
     TABLE_TYPE: BASE TABLE
         ENGINE: InnoDB
        VERSION: 10
     ROW_FORMAT: Dynamic
     TABLE_ROWS: 1
 AVG_ROW_LENGTH: 16384
    DATA_LENGTH: 16384
MAX_DATA_LENGTH: 0
   INDEX_LENGTH: 0
      DATA_FREE: 0
 AUTO_INCREMENT: NULL
    CREATE_TIME: 2022-09-22 08:18:38
    UPDATE_TIME: 2022-09-22 08:18:54
     CHECK_TIME: NULL
TABLE_COLLATION: latin1_swedish_ci
       CHECKSUM: NULL
 CREATE_OPTIONS: 
  TABLE_COMMENT: 
283 rows in set (0.02 sec)
```

​		COLUMNS     存储字段

```shell
*************************** 3083. row ***************************
           TABLE_CATALOG: def
            TABLE_SCHEMA: xingdian
              TABLE_NAME: t1
             COLUMN_NAME: id
        ORDINAL_POSITION: 1
          COLUMN_DEFAULT: NULL
             IS_NULLABLE: YES
               DATA_TYPE: int
CHARACTER_MAXIMUM_LENGTH: NULL
  CHARACTER_OCTET_LENGTH: NULL
       NUMERIC_PRECISION: 10
           NUMERIC_SCALE: 0
      DATETIME_PRECISION: NULL
      CHARACTER_SET_NAME: NULL
          COLLATION_NAME: NULL
             COLUMN_TYPE: int(11)
              COLUMN_KEY: 
                   EXTRA: 
              PRIVILEGES: select,insert,update,references
          COLUMN_COMMENT: 
   GENERATION_EXPRESSION: 
3083 rows in set (0.03 sec)
```

#### 2.创建库

方案一：交互式操作

```shell
mysql>  create database  xingdian;
```

数据库命名规则：

​		区分大小写

​		唯一性

​		不能使用关键字如 create select

​		不能单独使用数字		

方案二：非交互式

```shell
mysql -u root -pQianFeng@123 -e "create database diandian"
```

#### 3.查看数据库

```shell
mysql> show databases;
mysql> show create database xingdian;
mysql> select database(); 查看当前所在的库
```

#### 4.切换数据库

```shell
mysql> use xingdian;
```

#### 5.删除数据库

```shell
mysql> DROP DATABASE 数据库名;
```