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数据库SQLite的使用

      SQLite是一个C语言库,实现了一个小型、快速、独立、高可靠性、功能齐全的SQL数据库引擎SQLite文件格式稳定、跨平台且向后兼容。SQLite源代码属于公共领域(public-domain),任何人都可以免费将其用于任何目的。源码地址:https://github.com/sqlite/sqlite,最新发布版本为3.47.0。

      SQLite是关系型数据库,与许多其它数据库管理系统不同,SQLite不是一个客户端/服务器结构的数据库引擎,而是被集成在用户程序中。SQLite将整个数据库,包括定义、表、索引以及数据本身,作为一个单独的、可跨平台使用的文件存储在主机中

      SQLite提供了一个叫做sqlite3的独立程序用来查询和管理SQLite数据库文件,可从 https://www.sqlite.org/download.html 下载sqlite-tools-win-x64-3470000.zip获取到。

      所有的SQLite语句可以以任何关键字开始,如SELECT、INSERT、UPDATE、DELETE、ALTER、DROP等,所有的语句通常使用分号;结束

      Windows10上生成SQLite静态库:

      (1).从 https://www.sqlite.org/download.html 下载sqlite-dll-win-x64-3470000.zip和sqlite-amalgamation-3470000.zip

      (2).解压缩到同一目录下:此目录下有sqlite3.dll、sqlite3.def、sqlite3.h、sqlite3.c、sqlite3ext.h、shell.c

      (3).打开"Developer Command Prompt for VS 2022",并将其定位到存放sqlite的目录下,执行如下命令:执行完后会生成sqlite3.lib和sqlite3.exp

lib /DEF:sqlite3.def /OUT:sqlite3.lib /MACHINE:x64

      SQLite开源的可视化工具DB Browser for SQLite(DB4S)的使用:

      1.SQLite数据库浏览器(DB4S)是一款高质量、可视化、开源工具,用于创建、设计和编辑与SQLite兼容的数据库文件。源码地址:https://github.com/sqlitebrowser/sqlitebrowser,license为GPL或类似的开源许可证,最新发布版本为v3.13.1。它是跨平台的,可在Windows、Linux、MacOS等操作系统上使用。DB4S操作:

      (1).创建和压缩数据库文件

      (2).创建、定义、修改和删除表

      (3).创建、定义和删除索引

      (4).浏览、编辑、添加和删除记录(records)

      (5).搜索记录

      (6).以文本形式导入和导出记录

      (7).从CSV文件导入和导出表

      (8).从SQL转储文件(dump files)导入和导出数据库

      (9).SQL查询并检查结果

      2.Windows10上安装DB4S:

      (1).从https://github.com/sqlitebrowser/sqlitebrowser/releases/tag/v3.13.1 下载DB.Browser.for.SQLite-v3.13.1-win64.zip,并解压缩

      (2).双击打开DB Browser for SQLite.exe即可:界面如下:

     

      (1).SQLite是不区分大小写的,但也有一些命令是大小写敏感的。

      (2).SQLite没有一个单独的用于存储日期和/或时间的存储类,但SQLite能够把日期和时间存储为TEXT、REAL或INTEGER值。

      (3).在对当前数据库进行操作(c++)前,需要先关闭DB4S。

      (4).DB4S没有刷新功能,而PostgreSQL的图形界面(pgAdmin 4)有。

      以下为测试代码段

      (1).创建数据库:

int create_database(const std::string& dbname)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db); // 如果数据库不存在,则会创建它
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	sqlite3_close(db);
	return ret;
}

      (2).删除数据库:直接调用C++17中的std::filesystem::remove函数删除类似*.db的文件

int delete_database(const std::string& dbname)
{
	namespace fs = std::filesystem;
	fs::path file{ dbname };
	if (fs::exists(file)) {
		try {
			fs::remove(file);
		}
		catch (const fs::filesystem_error& e) {
			std::cerr << "Error: " << e.what() << std::endl;
			return -1;
		}
	} else {
		std::cerr << "Warning: database file does not exist: " << dbname << std::endl;
		return -1;
	}

	return 0;
}

      (3).创建表:

int create_table(const std::string& dbname, const std::string& command)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	char* errmsg{ nullptr };
	ret = sqlite3_exec(db, command.c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to create table: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

      (4).删除表:

int drop_table(const std::string& dbname, const std::string& tablename)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	char* errmsg{ nullptr };
	const std::string str{ "DROP TABLE " };
	ret = sqlite3_exec(db, (str+tablename).c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to drop table: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

      (5).向表中插入数据:

int insert_into_teacher(const std::string& dbname, int id, const std::string& name, const std::string& addr, const std::string& sex)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;
	
	char* errmsg{ nullptr };
	std::string str{ "INSERT INTO teacher (id, name, addr, sex) VALUES (" };
	str = str + std::to_string(id) + ", '" + name + "', '" + addr + "', '" + sex + "');";
	ret = sqlite3_exec(db, str.c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to insert into teacher: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

std::string get_current_time()
{
	auto timenow = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
	std::tm* now_tm = std::localtime(&timenow);
	std::ostringstream oss;
	oss << std::put_time(now_tm, "%Y-%m-%d %H:%M:%S");
	return oss.str();
}

int insert_into_student(const std::string& dbname, int id, const std::string& name, const std::string& addr, int age,
	float score, const std::string& date, const std::string& sex)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	char* errmsg{ nullptr };
	std::string str{ "INSERT INTO student (id, name, addr, age, score, date, sex) VALUES (" };
	str = str + std::to_string(id) + ", '" + name + "', '" + addr + "'," + std::to_string(age) + "," +
		std::to_string(score) + ", '" + date + "', '" + sex + "'); ";
	ret = sqlite3_exec(db, str.c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to insert into student: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

      (6).向已有表中添加、删除列:

int alter_table(const std::string& dbname)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	char* errmsg{ nullptr };
	const std::string str{ "ALTER TABLE teacher " };

	const std::string str1{ "ADD COLUMN hobbies CHAR(64) DEFAULT swim;" };
	ret = sqlite3_exec(db, (str+str1).c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to add cloumn: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	const std::string str2{ "DROP COLUMN addr;" };
	ret = sqlite3_exec(db, (str + str2).c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to drop column: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

      (7).删除表中数据:

int delete_table_data(const std::string& dbname)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	char* errmsg{ nullptr };
	const std::string str{ "DELETE FROM teacher WHERE id > 10000 OR sex='女';" };
	ret = sqlite3_exec(db, str.c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to delete data from teachar: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

      (8).调整表中已有数据:

int update_table_data(const std::string& dbname)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	char* errmsg{ nullptr };
	const std::string str1 = std::string("UPDATE teacher SET sex = 'man' WHERE sex = ") + "\'" + gbk_to_utf8("男") + "\';";
	ret = sqlite3_exec(db, str1.c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to update data from teachar: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	const std::string str2 = std::string("UPDATE teacher SET sex = ") + "\'" + gbk_to_utf8("女") + "\'" + " WHERE sex = 'woman';";
	ret = sqlite3_exec(db, str2.c_str(), nullptr, nullptr, &errmsg);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to update data from teachar: " << ret << ", " << errmsg << std::endl;
		sqlite3_free(errmsg);
	}

	sqlite3_close(db);
	return ret;
}

      (9).查询表中数据:

int select_table_data(const std::string& dbname)
{
	sqlite3* db{ nullptr };
	auto ret = sqlite3_open(dbname.c_str(), &db);
	if (ret != SQLITE_OK)
		std::cerr << "Error: fail to sqlite3_open: " << ret << ", " << sqlite3_errmsg(db) << std::endl;

	const std::string query{ "SELECT * FROM student WHERE age >= 20 AND DATETIME(date) > DATETIME('2024-11-07 17:54:30');" };
	char* errmsg{ nullptr };
	sqlite3_stmt* stmt{ nullptr };
	ret = sqlite3_prepare_v2(db, query.c_str(), -1, &stmt, 0);
	if (ret != SQLITE_OK) {
		std::cerr << "Error: fail to sqlite3_prepare_v2: " << ret << ", " << sqlite3_errmsg(db) << std::endl;
		return ret;
	}

	std::cout << "id\tname\taddr\tage\tscore\tdate\t\t\t\tsex" << std::endl;
	while (sqlite3_step(stmt) == SQLITE_ROW) {
		auto id = sqlite3_column_int(stmt, 0);
		auto name = utf8_to_gbk(std::string(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 1))));
		auto addr = utf8_to_gbk(std::string(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 2))));
		auto age = sqlite3_column_int(stmt, 3);
		auto score = sqlite3_column_double(stmt, 4);
		auto date = std::string(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 5)));
		auto sex = utf8_to_gbk(std::string(reinterpret_cast<const char*>(sqlite3_column_text(stmt, 6))));

		std::cout << id << "\t" << name << "\t" << addr << "\t" << age << "\t" << score << "\t"
			<< date << "\t\t" << sex << std::endl;
	}

	sqlite3_finalize(stmt);
	sqlite3_close(db);
	return ret;
}

      全局变量设置如下:

const std::string table_teacher{ "CREATE TABLE teacher ("
						"id INTEGER PRIMARY KEY NOT NULL CHECK(id>1000),"
						"name TEXT NOT NULL,"
						"addr TEXT DEFAULT 'BeiJing',"
						"sex TEXT NOT NULL);" };
const std::string table_student{ "CREATE TABLE student ("
						"id INTEGER PRIMARY KEY NOT NULL,"
						"name CHAR(32) NOT NULL,"
						"addr CHAR(64) DEFAULT 'TianJin',"
						"age INTEGER,"
						"score REAL,"
						"date CHAR(24),"
						"sex CHAR(8) NOT NULL);" };

      SQLite中没有实现类似libpqxx中的set_client_encoding函数,如果表中数据有中文则会显示乱码,这里实现utf8和gbk之间的转换:

inline std::string gbk_to_utf8(const std::string& str)
{
#ifdef _MSC_VER
	// gbk to wchar
	auto len = ::MultiByteToWideChar(CP_ACP, 0, str.c_str(), -1, nullptr, 0);
	std::wstring wstr(len, 0);
	::MultiByteToWideChar(CP_ACP, 0, str.c_str(), -1, &wstr[0], len);

	// wchar to utf8
	len = ::WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), -1, nullptr, 0, nullptr, nullptr);
	std::string u8str(len, 0);
	::WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), -1, &u8str[0], len, nullptr, nullptr);

	u8str.pop_back(); // remove '\0'
	return u8str;
#else
	return std::string{"Unimplemented"};
#endif
}

inline std::string utf8_to_gbk(const std::string& u8str)
{
#ifdef _MSC_VER
	// utf8 to wchar
	auto len = ::MultiByteToWideChar(CP_UTF8, 0, u8str.c_str(), -1, nullptr, 0);
	std::wstring wstr(len, 0);
	::MultiByteToWideChar(CP_UTF8, 0, u8str.c_str(), -1, &wstr[0], len);

	// wchar to gbk
	len = ::WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), -1, nullptr, 0, nullptr, nullptr);
	std::string str(len, 0);
	::WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), -1, &str[0], len, nullptr, nullptr);

	str.pop_back(); // remove '\0' 
	return str;
#else
	return std::string{"Unimplemented"};
#endif
}

      主函数如下:

int test_sqlite()
{
	const std::string dbname{ "info.db" };

	//create_database(dbname);
	delete_database(dbname);

	create_table(dbname, table_teacher);
	create_table(dbname, table_student);

	//drop_table(dbname, "teacher");
	//drop_table(dbname, "student");

	insert_into_teacher(dbname, 1111, gbk_to_utf8("Tom"), gbk_to_utf8("HeBei"), gbk_to_utf8("man"));
	insert_into_teacher(dbname, 5555, gbk_to_utf8("Tom"), gbk_to_utf8("北京"), gbk_to_utf8("男"));
	insert_into_teacher(dbname, 2222, gbk_to_utf8("小张"), gbk_to_utf8("天津"), gbk_to_utf8("woman"));
	insert_into_teacher(dbname, 16625, gbk_to_utf8("小王"), gbk_to_utf8("Tianjin"), gbk_to_utf8("女"));

	insert_into_student(dbname, 8, gbk_to_utf8("小王"), gbk_to_utf8("HeBei"), 32, 88.8f, get_current_time(), gbk_to_utf8("男"));
	insert_into_student(dbname, 28, gbk_to_utf8("小何"), gbk_to_utf8("深圳"), 8, 22.22f, get_current_time(), gbk_to_utf8("女"));
	std::this_thread::sleep_for(std::chrono::minutes(1));
	insert_into_student(dbname, 29, gbk_to_utf8("Lucy"), gbk_to_utf8("北京"), 18, 22.22f, get_current_time(), gbk_to_utf8("woman"));
	insert_into_student(dbname, 33, gbk_to_utf8("Tom"), gbk_to_utf8("深圳"), 28, 22.22f, get_current_time(), gbk_to_utf8("woman"));
	insert_into_student(dbname, 18, gbk_to_utf8("小李"), gbk_to_utf8("上海"), 28, 66.6f, get_current_time(), gbk_to_utf8("女"));
	std::this_thread::sleep_for(std::chrono::seconds(5));
	insert_into_student(dbname, 48, gbk_to_utf8("Tom"), gbk_to_utf8("深圳"), 38, 22.22f, get_current_time(), gbk_to_utf8("woman"));

	alter_table(dbname);
	delete_table_data(dbname);
	update_table_data(dbname);
	select_table_data(dbname);

	return 0;
}

      执行结果如下:

      DB4S显示内容如下:

      GitHubhttps://github.com/fengbingchun/Messy_Test

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