嵌入式(数据库开发)

本文介绍SQLite数据库的基本操作,包括安装、常用命令、SQL语句使用及C语言API编程示例。涵盖表的增删改查等常见任务。

【1】数据库

1, 数据库的安装
sudo dpkg -i *.deb(本地)
sudo apt-get install sqlite3

2, 数据库命令:
1)系统命令 , 都以’.'开头
.exit
.quit
.table 查看表
.schema 查看表的结构

  2)sql语句, 都以‘;’结尾

    1-- 创建一张表
        create table stuinfo(id integer, name text, age integer, score float);
    
    2-- 插入一条记录
        insert into stuinfo values(1001, 'zhangsan', 18, 80);  //全部字段插入
        insert into stuinfo (id, name, score) values(1002, 'lisi', 90);  //部分字段插入

    3-- 查看数据库记录
  
        select * from stu;  //查询所有字段
         select name,socre from stu;  //查name和socre
        select * from stuinfo where score = 80;
        select * from stuinfo where score = 80 and name= 'zhangsan';   //同时满足
        select * from stuinfo where score = 80 or name='wangwu';		
        select name,score from stuinfo;  查询指定的字段 
        select * from stuinfo where score >= 85 and score < 90;

    4-- 删除一条记录
        delete from stuinfo where id=1003 and name='zhangsan';

    5-- 更新一条记录
        update stuinfo set age=20 where id=1003;
        update stuinfo set age=30, score = 82 where id=1003;

    6-- 删除一张表
        drop table stuinfo;

    7-- 增加一列
        alter table stuinfo add column sex char;

    8-- 删除一列
      
      (1)创建一张新的表 				   create table stu as select id, name, score from stuinfo;
      (2)删除原有的表    			   drop table stuinfo;
      (3)将新的表名字改成原有的旧表的名字  alter table stu rename to stuinfo;

 数据库设置主键:
 create table info(id integer primary key autoincrement, name vchar);

【3 】sqlite3 数据库 C语言 API

```c
 int sqlite3_open(
 const char *filename,   /* Database filename (UTF-8) */
 sqlite3 **ppDb          /* OUT: SQLite db handle */
 );
    功能:打开数据库
    参数:filename  数据库路径名称
          ppdb      数据库的操作句柄句柄
    返回值:成功为0 SQLITE_OK ,出错 错误码
   int sqlite3_close(sqlite3* db);
功能:关闭数据库
参数:db操作数据库的指针
返回值:成功为0 SQLITE_OK ,出错 错误码
   const char *sqlite3_errmsg(sqlite3*db);
功能:得到错误信息的描述
   int sqlite3_exec(
   sqlite3* db,                                  /* An open database */
   const char *sql,                           /* SQL to be evaluated */
   int (*callback)(void* arg,int,char**,char**),  /* Callback function */
   void * arg,                                    /* 1st argument to      
   callback */
   char **errmsg                              /* Error msg written here */
  );

功能:执行一条sql语句
参数:db 数据库句柄
sql sql 一条sql语句
callback 回调函数,只有在查询时,才传参
arg 为回调函数传递参数
errmsg 错误消息
返回值:成功 SQLITE_OK

查询回调函数:

int (*callback)(void* arg,int ncolumns ,char** f_value,char** f_name),  /* Callback function */

功能:查询语句执行之后,会回调此函数
参数:arg 接收sqlite3_exec 传递来的参数
ncolumns 列数
f_value 列的值得地址
f_name 列的名称
返回值:0,

int sqlite3_get_table
(
  sqlite3 *db,          /* An open database */
  const char *zSql,     /* SQL to be evaluated */
  char ***pazResult,    /* Results of the query */
  int *pnRow,           /* Number of result rows written here */
  int *pnColumn,        /* Number of result columns written here */
  char **pzErrmsg       /* Error msg written here */
);
void sqlite3_free_table(char **result);

查询

#include <stdio.h>
#include <sqlite3.h>
#include <stdlib.h>
#include <unistd.h>

#define  DATABASE   "student.db"

int do_insert(sqlite3 *db)
{
	char sql[128] = {};
	int id;
	char name[20];
	float score;
	char *errmsg;

	printf("Input id:");
	scanf("%d", &id);
	getchar();

	printf("Input name:");
	scanf("%s", name);
	getchar();

	printf("Input score:");
	scanf("%f", &score);
	getchar();

	sprintf(sql,"insert into stuinfo values(%d,'%s',%f);", id, name, score);

	if(sqlite3_exec(db, sql,NULL ,NULL ,&errmsg) != SQLITE_OK)
	{
		printf("%s,%d --> %s\n", __func__, __LINE__, errmsg);
		return -1;
	}
	else
	{
		printf("Insert done.\n");
	}

	return 0;
}

int callback(void* arg,int ncolumns ,char** f_value,char** f_name)
{
	int i = 0;
	for(i = 0; i < ncolumns; i++)
	{
		printf("%-13s ", f_value[i]);
	}
	putchar(10);

	puts("++++++++++++++++");

	return 0;
}

int do_query(sqlite3 *db)
{
	char sql[128] = {};
	int id;
	char *errmsg;

#if 0
	printf("Input id:");
	scanf("%d", &id);
	getchar();

	sprintf(sql,"select * from stuinfo where id = %d;", id);
#endif
#if 1
	sprintf(sql,"select * from stuinfo;");
#endif
	if(sqlite3_exec(db, sql,callback ,NULL ,&errmsg) != SQLITE_OK)
	{
		printf("%s,%d --> %s\n", __func__, __LINE__, errmsg);
		return -1;
	}
	else
	{
		printf("Query done.\n");
	}
	return 0;
}

// gcc stu.c -o stu -lsqlite3
int main(int argc, const char *argv[])
{
	sqlite3 * db;
	char *errmsg;
	int n = 0;
	
	if(sqlite3_open(DATABASE, &db) != SQLITE_OK)
	{
		printf("%s\n", sqlite3_errmsg(db));
		return -1;
	}
	else 
	{
		printf("Create or open success.\n");
	}

	if(sqlite3_exec(db, "create table if not exists stuinfo (id integer, name vchar(20) not null,score float);",\
				NULL, NULL,&errmsg) != SQLITE_OK)
	{
		printf("%s\n", errmsg);
	}
	
	while(1)
	{
		printf("*******************************************************\n");
		printf("1,insert  2,delete  3,select  4,update 5,quit         \n");
		printf("*******************************************************\n");

		printf("Input:");

		scanf("%d",&n);
		switch(n)
		{
		case 1:
			do_insert(db);
			break;
		case 2:
		//	do_delete();
			break;
		case 3:
		//	do_query1(db);
			do_query(db);
			break;
		case 4:
		//	do_update();
			break;
		case 5:
			sqlite3_close(db);
			exit(0);
			break;
		default:
			printf("Invalid  cmd.\n");

		}

	}
	
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sqlite3.h>

#define  DATABASE  "student.db"
#define  N  128

int do_insert(sqlite3 *db)
{
	int id;
	char name[32] = {};
	char sex;
	int score;
	char sql[N] = {};
	char *errmsg;

	printf("Input id:");
	scanf("%d", &id);

	printf("Input name:");
	scanf("%s", name);
	getchar();

	printf("Input sex:");
	scanf("%c", &sex);

	printf("Input score:");
	scanf("%d", &score);

	sprintf(sql, "insert into stu values(%d, '%s', '%c', %d)", id, name, sex, score);

	if(sqlite3_exec(db, sql, NULL, NULL, &errmsg) != SQLITE_OK)
	{
		printf("%s\n", errmsg);
	}
	else
	{
		printf("Insert done.\n");
	}

	return 0;
}
int do_delete(sqlite3 *db)
{
	int id;
	char sql[N] = {};
	char *errmsg;

	printf("Input id:");
	scanf("%d", &id);

	sprintf(sql, "delete from stu where id = %d", id);

	if(sqlite3_exec(db, sql, NULL, NULL, &errmsg) != SQLITE_OK)
	{
		printf("%s\n", errmsg);
	}
	else
	{
		printf("Delete done.\n");
	}

	return 0;
}
int do_update(sqlite3 *db)
{
	int id;
	char sql[N] = {};
	char name[32] = "zhangsan";
	char *errmsg;

	printf("Input id:");
	scanf("%d", &id);

	sprintf(sql, "update stu set name='%s' where id=%d", name,id);

	if(sqlite3_exec(db, sql, NULL, NULL, &errmsg) != SQLITE_OK)
	{
		printf("%s\n", errmsg);
	}
	else
	{
		printf("update done.\n");
	}
	return 0;
}

int callback(void *arg, int f_num, char ** f_value, char ** f_name)
{
	int i = 0;

	for(i = 0; i < f_num; i++)
	{
	//	printf("%-8s %s", f_value[i], f_name[i]);
		printf("%-8s", f_value[i]);
	}

	printf("++++++++++++++++++++++");
	putchar(10);

	return 0;
}

int do_query(sqlite3 *db)
{
	char *errmsg;
	char sql[N] = "select count(*) from stu where name='zhangsan';";

	if(sqlite3_exec(db, sql, callback,NULL , &errmsg) != SQLITE_OK)
	{
		printf("%s", errmsg);
	}
	else
	{
		printf("select done.\n");
	}
}

int do_query1(sqlite3 *db)
{
	char *errmsg;
	char ** resultp;
	int nrow;
	int ncolumn;

	if(sqlite3_get_table(db, "select * from stu", &resultp, &nrow, &ncolumn, &errmsg) != SQLITE_OK)
	{
		printf("%s\n", errmsg);
		return -1;
	}
	else
	{
		printf("query done.\n");
	}

	int i = 0;
	int j = 0;
	int index = ncolumn;

	for(j = 0; j < ncolumn; j++)
	{
		printf("%-10s ", resultp[j]);
	}
	putchar(10);

	for(i = 0; i < nrow; i++)
	{
		for(j = 0; j < ncolumn; j++)
		{
			printf("%-10s ", resultp[index++]);
		}
		putchar(10);
	}

return 0;
}

int main(int argc, const char *argv[])
{
	sqlite3 *db;
	char *errmsg;
	int n;
	
	if(sqlite3_open(DATABASE, &db) != SQLITE_OK)
	{
		printf("%s\n", sqlite3_errmsg(db));
		return -1;
	}
	else
	{
		printf("open DATABASE success.\n");
	}

	if(sqlite3_exec(db, "create table if not exists stu(id int, name char , sex char , score int);",
				NULL, NULL, &errmsg) != SQLITE_OK)
	{
		printf("%s\n", errmsg);
	}
	else
	{
		printf("Create or open table success.\n");
	}

	while(1)
	{
		printf("********************************************\n");
		printf("1: insert  2:query  3:delete 4:update 5:quit\n");
		printf("********************************************\n");
		printf("Please select:");
		scanf("%d", &n);

		switch(n)
		{
			case 1:
				do_insert(db);
				break;
			case 2:
				do_query(db);
			//	do_query1(db);
				break;
			case 3:
				do_delete(db);
				break;
			case 4:
				do_update(db);
				break;
			case 5:
				printf("main exit.\n");
				sqlite3_close(db);
				exit(0);
				break;
			default :
				printf("Invalid data n.\n");
		}
	}
	return 0;
}

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