在Qt中使用SQLite数据库

JdSnE27zv

38人浏览 · 2026-06-10 00:03:21

JdSnE27zv · 2026-06-10 00:03:21 发布

前言

SQLite（sql）是一款开源轻量级的数据库软件，不需要server，可以集成在其他软件中，非常适合嵌入式系统。
Qt5以上版本可以直接使用SQLite（Qt自带驱动）。

用法

1 准备

引入SQL模块
在Qt项目文件(.pro文件)中，加入SQL模块：

QT += sql

引用头文件
在需要使用SQL的类定义中，引用相关头文件。例如：

#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>

CPP 复制全屏

2 使用

1. 建立数据库

检查连接、添加数据库驱动、设置数据库名称、数据库登录用户名、密码。

QSqlDatabase database;
if (QSqlDatabase::contains("qt_sql_default_connection"))
{
    database = QSqlDatabase::database("qt_sql_default_connection");
}
else
{
    database = QSqlDatabase::addDatabase("QSQLITE");
    database.setDatabaseName("MyDataBase.db");
    database.setUserName("XingYeZhiXia");
    database.setPassword("123456");
}

上述代码解释：
（1）第一行中，建立了一个QSqlDatabase对象，后续的操作要使用这个对象。
（2）if语句用来检查指定的连接(connection)是否存在。这里指定的连接名称（connection name）是qt_sql_default_connection，这是Qt默认连接名称。实际使用时，这个名称可以任意取。如果判断此连接已经存在，那么QSqlDatabase::contains()函数返回true。此时，进入第一个分支，QSqlDatabase::database()返回这个连接。
（3）如果这个连接不存在，则进入else分支，需要创建连接，并添加数据库。在else分支第一行，addDatabase()的参数QSQLITE是SQLite对应的驱动名，不能改。而且需要注意的是，addDatabase()的第二个参数被省略了，第二个参数的默认参数就是上面提到的Qt默认连接名称qt_sql_default_connection。如果需要使用自定义的连接名称（如果程序需要处理多个数据库文件的话就会这样），则应该加入第二个参数，例如

database = QSqlDatabase::addDatabase("QSQLITE", "my_sql_connection);

这个时候，如果在另一个地方需要判断my_sql_connection连接是否存在，就应该使用if (QSqlDatabase::contains("my_sql_connection"))。
（4）else分支第二行中，setDatabaseName()的参数是数据库文件名。如果这个数据库不存在，则会在后续操作时自动创建；如果已经存在，则后续的操作会在已有的数据库上进行。
（5）else分支后面两行，设置用户名和密码。用户名，密码都可以随便取，也可以省略。

2. 打开数据库

使用open()打开数据库，并判断是否成功。注意，在第一步检查连接是否存在时，如果连接存在，则在返回这个连接的时候，会默认将数据库打开。

if (!database.open())
{
    qDebug() << "Error: Failed to connect database." << database.lastError();
}
else
{
    // do something
}

如果打开成功，则进入else分支。对数据库的操作都需要在else分支中进行。

3. 关闭数据库

数据库操作完成后，最好关闭。

    database.close();

4. 操作数据库

对数据库进行操作需要用到QSqlQuery类，操作前必须定义一个对象。下面举例说明操作方法。操作需要使用SQLite语句，本文中的几个例子会使用几个常用的语句，关于SQLite语句的具体信息请参考SQLite相关资料。
例1：创建表格
创建一个名为student的表格，表格包含三列，第一列是id，第二列是名字，第三列是年龄。

QSqlQuery sql_query;
QString create_sql = "create table student (id int primary key, name varchar(30), age int)";
sql_query.prepare(create_sql);
if(!sql_query.exec())
{
    qDebug() << "Error: Fail to create table." << sql_query.lastError();
}
else
{
    qDebug() << "Table created!";
}

代码解释：
（1）第一行定义一个QSqlQuery对象。
（2）第二行是一个QString，其中的内容是SQLite语句。对数据库的操作，都是用SQLite的语句完成的，把这些指令以QString类型，通过prepare函数，保存在QSqlQuery对象中。也可将指令，以QString形式直接写在exec()函数的参数中，例如：

    sql_query.exec("create table student (id int primary key, name varchar(30), age int)");

创建表格语句：create table <table_name> (f1 type1, f2 type2,…);
create table是创建表格的语句，也可用大写CREATE TABLE；student是表格的名称，可以任意取；括号中是表格的格式，上述指令表明，表格中有三列，第一列的名称（表头）是id，这一列储存的数据类型是int，第二列名称是name，数据类型是字符数组，最多有30个字符（和char(30)的区别在于，varchar的实际长度是变化的，而char的长度始终是给定的值），第三列的名称是age，数据类型是int。
如果sql_query.exec()执行成功，则创建表格成功。

例2：插入数据
在刚才创建的表格中，插入一行数据。

QString insert_sql = "insert into student values (?, ?, ?)";
sql_query.prepare(insert_sql);
sql_query.addBindValue(max_id+1);
sql_query.addBindValue("Wang");
sql_query.addBindValue(25);
if(!sql_query.exec())
{
    qDebug() << sql_query.lastError();
}
else
{
    qDebug() << "inserted Wang!";
}
if(!sql_query.exec("INSERT INTO student VALUES(3, \"Li\", 23)"))
{
    qDebug() << sql_query.lastError();
}
else
{
    qDebug() << "inserted Li!";
}

插入语句：insert into <table_name> values (value1, value2,…);
insert into是插入语句，student是表格名称，values()是要插入的数据。这里，我们插入了2组数据。插入第一组数据的时候，用addBindValue来替代语句中的?，替代的顺序与addBindValue调用的顺序相同。插入第二组数据的时候，则是直接写出完整语句。

例3：更新数据（修改数据）

QString update_sql = "update student set name = :name where id = :id";
sql_query.prepare(update_sql);
sql_query.bindValue(":name", "Qt");
sql_query.bindValue(":id", 1);
if(!sql_query.exec())
{
    qDebug() << sql_query.lastError();
}
else
{
    qDebug() << "updated!";
}

语句：update <table_name> set <f1=value1>, <f2=value2>… where <expression>;
更新（修改）的语句是update...set...，其中student是表格名称，name是表头名称（即第二列），:name是待定的变量，where用于确定是哪一组数据，:id也是待定变量。
bindValue(" ", " ")函数用来把语句中的待定变量换成确定值。

例4：查询数据
（1）查询部分数据

QString select_sql = "select id, name from student";
if(!sql_query.exec(select_sql))
{
    qDebug()<<sql_query.lastError();
}
else
{
    while(sql_query.next())
    {
        int id = sql_query.value(0).toInt();
        QString name = sql_query.value(1).toString();
        qDebug()<<QString("id:%1    name:%2").arg(id).arg(name);
    }
}

语句select <f1>, <f2>, ... from <table_name>;
select是查询指令；<f1> 等等是要查询的变量（即表头），中间用逗号隔开；from ...指定表格。
上述语句是说查询student表中的 id 和 name 。执行查询之后，用sql_query.value(int)来获得数据。同样地，value(0)表示第一个数据，即 id，value(1)表示name。注意：value()函数的返回值类型是QVariant，因此要用toInt()等函数转换成特定的类型。
（2）查询全部数据

QString select_all_sql = "select * from student";
sql_query.prepare(select_all_sql);
if(!sql_query.exec())
{
    qDebug()<<sql_query.lastError();
}
else
{
    while(sql_query.next())
    {
        int id = sql_query.value(0).toInt();
        QString name = sql_query.value(1).toString();
        int age = sql_query.value(2).toInt();
        qDebug()<<QString("id:%1    name:%2    age:%3").arg(id).arg(name).arg(age);
    }
}

语句select * from <table_name>;
查询所有数据用 * 表示。用while(sql_query.next())用来遍历所有行。同样用value()获得数据。
（3）查询最大id

QString select_max_sql = "select max(id) from student";
int max_id = 0;
sql_query.prepare(select_max_sql);
if(!sql_query.exec())
{
    qDebug() << sql_query.lastError();
}
else
{
    while(sql_query.next())
    {
        max_id = sql_query.value(0).toInt();
        qDebug() << QString("max id:%1").arg(max_id);
    }
}

这个就是在语句中用max来获取最大值。

例5：删除与清空
（1）删除一条数据

QString delete_sql = "delete from student where id = ?";
sql_query.prepare(delete_sql);
sql_query.addBindValue(0);
if(!sql_query.exec())
{
    qDebug()<<sql_query.lastError();
}
else
{
    qDebug()<<"deleted!";
}

语句delete from <table_name> where <f1> = <value>
delete用于删除条目，用where给出限定条件。例如此处是删除 id = 0的条目。
（2）清空表格（删除所有）

QString clear_sql = "delete from student";
sql_query.prepare(clear_sql);
if(!sql_query.exec())
{
    qDebug() << sql_query.lastError();
}
else
{
    qDebug() << "table cleared";
}

这里没有用where给出限制，就会删除所有内容。

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