嵌入式学习第二十八天！（数据库）-编程知识

数据库：

1. 数据库软件：

1. 关系型数据库：Mysql、Oracle、SqlServer、Sqlite

2. 非关系型数据库：Redis、NoSQL

2. 数组、链表、文件、数据库

数组、链表：内存存放数据的方式（代码运行结束、关机数据丢失）

文件、数据库：外存存放数据的方式（代码运行结束、关机数据不会丢失）

文件：数据量很小，处理效率很低

数据库：数据量很大，处理数据（增删改查）效率高

3. 安装Sqlite数据库：

1. 让虚拟机能够哦上网

2. apt-get工具集配置好

3. sudo apt-get install sqlite3

4. 启动sqlite3

sqlite3

5. 输入.quit退出

4. SQL命令：

1. 打开/关闭数据库中列名称

.headers on/off

2. 设置输出模式，MODE可以是csv逗号分隔的值、column左对齐的列等

.mode csv/column/html/insert/line/list/tabs/tcl

3. 查看表名对应的表的形式（有哪几列？每一列类型？）

.schema 表名称

4. 设置显示时的数据宽带

.width 宽度

5. 查看数据库文件中的所有表

.tables

这里只展示了几个常用的命令，其他命令可以查看SQLite参考手册中的SQLite命令

5. SQL语言：

数据的：增、删、改、查

1. 使用sqlite3打开数据库文件

sqlite3 数据库文件名
eg: sqlite3 ./student.db

2. 创建/删除表：

create table 表名
eg:sqlite> create table student (id integer primary key asc, name varchar(255), sex varchar(32), age integer, score integer);drop table 表名
eg:sqlite> drop table student

3. 插入数据：

insert into
eg:sqlite> insert into student values (1001, "张三", "男", 19, 80);sqlite> insert into student (id, name, score) values (1002, "李四", 100);sqlite> insert into student values (1002, "王二", "女", 18, NULL);

4. 查找数据：

select
eg:sqlite> select * from student;sqlite> select name, score from student;

5. 内容匹配：

where
eg:sqlite> select * from student where name like "%张%";

练习:数据库完成对订单的管理:

1. 创建一张订单表,由 ID, 订单号, 货物信息, 生产厂商, 联系人, 联系电话, 订单时间

sqlite> create table older_manage...> (ID integer,...> ordername varchar(32),...> orderinfo varchar(50),...> factoryname varchar(50),...> contactperson varchar(32),...> contactphone varchar(32),...> oldertime varchar(32));

2. 在表中插入随机给定的10条数据

sqlite> insert into older_manage values(1, "D202403120001", "Mate60 手机", "华为", "张三", "19829147641", "20240312 22:04:00");
sqlite> insert into older_manage values(2, "D202403120002", "Mate 平板", "华为", "张三", "13819724571", "20240312 18:34:10");
sqlite> insert into older_manage values(3, "D202403120003", "GTWatch 手表", "华为", "张三", "13947231554", "20240312 10:14:15");
sqlite> insert into older_manage values(4, "D202403120004", "Iphone14 手机", "苹果", "李四", "13145721214", "20240311 12:31:42");
sqlite> insert into older_manage values(5, "D202403120005", "Ipad 平板", "苹果", "李四", "13147561243", "20240311 13:13:12");
sqlite> insert into older_manage values(6, "D202403120006", "Iwatch 手表", "苹果", "李四", "13147561478", "20240310 11:13:12");
...

3. 查找联系人为 "张三" 的所有订单号

select ordername from older_manage where contactperson="张三";

查找订单号为 "D202403120001" 的所有订单信息

select * from older_manage where oldername="D202403120001"；

查找订单时间截止到当天的所有订单号及联系人、联系电话

select oldername,contactperson,contactphone from older_manage where oldertime<"20240311 24:00:00";

查找货物信息包含 "手机" 内容的所有订单信息及货物信息

select oldername,olderinfo from older_manage where olderinfo like "%手机%";

查找生产厂商是"华为" 的所有货物信息包含 "平板" 的订单信息

select * from order_manage where factoryname="华为" and orderinfo like "%d平板%";

6. 主键：

key：键值

內键：在表中唯一标识一条数据称为內键

外键：与外部表进行标识的数据称为外键

7. 删除：

delete from
eg:delete from student where name="李四";

8. 修改：

update
eg:update student set sex="男", age="19" where name "王二";

9. 排序：

older by
eg:select * from order_manage order by ordertime desc;

10. 多表联合查询：

1. 交叉连接：

cross join
eg:sqlite> select student.name as 学生姓名, lesson.name as 课程名...> from score cross join lesson;

2. 内连接：

inner join
eg:sqlite> select score.id as 成绩编号, student.name as 学生姓名, score.score as 成绩        ...> from score inner join student on score.stuid=student.id;

3. 外连接：

outer join
eg:sqlite> select score.id as 成绩编号, student.name as 学生姓名, score.score as 成绩...> from student left outer join score on score.stuid=stdent.id;

示例：

sqlite> select score.id as 成绩编号, student.name as 学生姓名, score.score as 成绩...> from student left outer join score on score.stuid=student.id...> where name="张三"...> order by 成绩 desc;

作业：

1. 从终端输入一个单词，在文件中查找单词含义并打印在终端：

#include <stdio.h>
#include <string.h>int main(void)
{FILE * fd = NULL;char str[64] = {0};char tmpbuff[1024] = {0};char *pread = NULL;char *pstr = NULL;fd = fopen("dict.txt", "r");if(fd == NULL){perror("fail to fopen");return -1;}while(1){gets(str);if(!strcmp(str, ".quit")){break;}while(1){pread = fgets(tmpbuff, sizeof(tmpbuff), fd);if(pread == NULL){perror("fail to fgets");rewind(fd);break;}pstr = pread;while(*pread != ' ' && *pread != '\0'){pread++;}*pread = '\0';pread++;if(!strcmp(str, pstr)){while(*pread == ' '){pread++;}printf("%s\n", pread);rewind(fd);break;}}}fclose(fd);return 0;
}

2. 1037 在霍格沃茨找零钱 - PAT (Basic Level) Practice （中文） (pintia.cn)

#include <stdio.h>struct money
{int Galleon;int Sickle;int Knut;
};void IntMoneyInfo(struct money *pay)
{scanf("%d.%d.%d", &pay->Galleon, &pay->Sickle, &pay->Knut);return;
}void CountMoney(struct money pmax, struct money pmin, int *galleon, int *sickle, int *knut)
{*knut = pmax.Knut - pmin.Knut;if(*knut < 0){pmax.Sickle -= 1;*knut = (pmax.Knut + 29) - pmin.Knut;}*sickle = pmax.Sickle - pmin.Sickle;if(*sickle < 0){pmax.Galleon -= 1;*sickle = (pmax.Sickle + 17) - pmin.Sickle;}*galleon = pmax.Galleon - pmin.Galleon;return;
}int main(void)
{int galleon = 0;int sickle = 0;int knut = 0;struct money accountspay;struct money actualpay;IntMoneyInfo(&accountspay);IntMoneyInfo(&actualpay);if(actualpay.Galleon > accountspay.Galleon){CountMoney(actualpay, accountspay, &galleon, &sickle, &knut);printf("%d.%d.%d\n", galleon, sickle, knut);}else{CountMoney(accountspay, actualpay, &galleon, &sickle, &knut);printf("-%d.%d.%d\n", galleon, sickle, knut);}return 0;
}