SQLite3数据库学习
前言
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基于嵌入式Linux的数据库主要有SQLite,Firebird,Berkeley DB等。其中sQLite的源代码是c,其源代码完全开放。SQLite第一个A1pha版本诞生于2000年5月。他是一个轻量级的嵌入式数据库。sQLite有以下特性:零配置一无需安装和管理配置;储存在单一磁盘文件中的一个完整的数据库;数据库文件可以在不同字节顺序的机器间自由共享;支持数据库大小至2TB;足够小,全部源码大致3万行c代码,250KB;比目前流行的大多数数据库对数据的操作要快;
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一、安装方式
sudo apt-get install sqlite3
二、sqlite3基本命令
1、系统命令(以‘.’开头的命令)
.help 帮助
.quit 退出
.exit 退出
.schema 查看表的结构图
2、sql命令
基本的sql命令,不以.
开头,但是都要以;
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);
insert into stuinfo (id, name, score) values(1002, ‘lisi’, 90);
3-- 查看数据库记录
select * from stuinfo;
select * from stuinfo where score = 80;
select * from stuinfo where score = 80 and name= ‘zhangsan’;
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
create table stu as select id, name, score from stuinfo;
drop table stuinfo;
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
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 数据库名称
ppdb 数据库句柄
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:
返回值:成功为0 SQLITE_OK ,出错 错误码
== const char sqlite3_errmsg(sqlite3db);==
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
3.基于sqlite3的简易学生管理系统
代码如下(示例):
#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;
}