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: 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
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：
set型数据是不允许被重复使用的
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: 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
修改数据类型或约束条件：
ALTER TABLE 表名 MODIFY 字段名 新数据类型 [完整性约束条件…];
修改字段名，数据类型，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: 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
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
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: 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
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
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: 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
*************************** 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
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: 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
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;