Day 24 数据库管理及数据类型-编程知识

数据库管理及数据类型

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

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

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

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

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

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：

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：

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：

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：

mysql> insert into student1(id,name,sex,age) values(1,'xingdia','m','26');

查看表结构：

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：

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：

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: 0mysql> 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

               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：

mysql> create table student2(id int,name varchar(50),         born_year year,birthday date,class_time time,reg_time datetime );

插入数据：

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

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：

mysql> create table student3(id int,name varchar(50),sex enum('male','female'),hobby set('music','book','game','disc'));

查看表结构：

mysql> desc student3;
mysql> show create table student3\G

插入数据：

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

DESCRIBE 表名;
DESC 表名;

查看表详细结构

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

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）

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）

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：

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：

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：

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）

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：

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：

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: 0MySQL [(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 字段名新数据类型 [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

mysql> alter table service engine=innodb;     //engine=myisam|memory|....

2.添加字段

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

mysql> alter table student10 drop sex;

4.修改字段类型

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: 0MySQL [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: 0MySQL [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

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: 0MySQL [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 keyMySQL [school]> alter table student10 modify id int not null auto_increment;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0MySQL [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

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

MySQL [school]> alter table student1 modify id int  auto_increment;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0MySQL [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

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: 0MySQL [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: 0MySQL [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

mysql> create table new_service select * from service;

只复制表结构

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

mysql> create table t4 like employees;

10.删除表

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

mysql> update student set name='123' where id=1;

删除某一行：

delete from 表名 where id=1

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

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

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

MySQL [information_schema]> select * from information_schema.TABLES\G
*************************** 283. row ***************************TABLE_CATALOG: defTABLE_SCHEMA: xingdianTABLE_NAME: t1TABLE_TYPE: BASE TABLEENGINE: InnoDBVERSION: 10ROW_FORMAT: DynamicTABLE_ROWS: 1AVG_ROW_LENGTH: 16384DATA_LENGTH: 16384
MAX_DATA_LENGTH: 0INDEX_LENGTH: 0DATA_FREE: 0AUTO_INCREMENT: NULLCREATE_TIME: 2022-09-22 08:18:38UPDATE_TIME: 2022-09-22 08:18:54CHECK_TIME: NULL
TABLE_COLLATION: latin1_swedish_ciCHECKSUM: NULLCREATE_OPTIONS: TABLE_COMMENT: 
283 rows in set (0.02 sec)

COLUMNS 存储字段

*************************** 3083. row ***************************TABLE_CATALOG: defTABLE_SCHEMA: xingdianTABLE_NAME: t1COLUMN_NAME: idORDINAL_POSITION: 1COLUMN_DEFAULT: NULLIS_NULLABLE: YESDATA_TYPE: int
CHARACTER_MAXIMUM_LENGTH: NULLCHARACTER_OCTET_LENGTH: NULLNUMERIC_PRECISION: 10NUMERIC_SCALE: 0DATETIME_PRECISION: NULLCHARACTER_SET_NAME: NULLCOLLATION_NAME: NULLCOLUMN_TYPE: int(11)COLUMN_KEY: EXTRA: PRIVILEGES: select,insert,update,referencesCOLUMN_COMMENT: GENERATION_EXPRESSION: 
3083 rows in set (0.03 sec)

2.创建库

方案一：交互式操作

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

mysql -u root -pQianFeng@123 -e "create database diandian"

3.查看数据库

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

mysql> use xingdian;

5.删除数据库

mysql> DROP DATABASE 数据库名;

       NUMERIC_SCALE: 0DATETIME_PRECISION: NULLCHARACTER_SET_NAME: NULLCOLLATION_NAME: NULLCOLUMN_TYPE: int(11)COLUMN_KEY: EXTRA: PRIVILEGES: select,insert,update,referencesCOLUMN_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

mysql -u root -pQianFeng@123 -e "create database diandian"

3.查看数据库

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

mysql> use xingdian;

5.删除数据库

mysql> DROP DATABASE 数据库名;