Qt5連接Mysql數據庫及常見報錯解決方法

首先要在.pro文件中加入sql

QT       += core gui sql

引入頭文件

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

建立並打開數據庫

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");	//添加數據庫名稱，這裏寫QMYSQL
db.setHostName("127.0.0.1");	//設置數據庫主機名
db.setDatabaseName("Mydb");	//設置數據庫名
db.setUserName("root");	//設置數據庫用戶名
db.setPassword("123456");	//設置數據庫密碼
if (!db.open())
{
	qDebug() << "Error: Failed to connect database." << db.lastError();
}
else
{
 	qDebug() << "Succeed to connect database." ;
}

創建表

QSqlQuery sql_query;
    if(!sql_query.exec("create table allfilesdata(  \
                       fileid INTEGER primary key AUTOINCREMENT,    \
                       filename text UNIQUE,  \
                       filepath  text NOT NULL, \
                       filesize INTEGER, \
                       fileattributes INTEGER NOT NULL, \
                       creat_dwlowtime INTEGER NOT NULL,    \
                       creat_dwhightime INTEGER NOT NULL,   \
                       lastaccess_dwlowtime INTEGER NOT NULL,   \
                       lastaccess_dwhightime INTEGER NOT NULL,  \
                       lastwrite_dwlowtime INTEGER NOT NULL,    \
                       lastwrite_dwhightime INTEGER NOT NULL)"))
    {
        qDebug() << "Error: Fail to create table."<< sql_query.lastError();
    }
    else
    {
        qDebug() << "Table created!";
    }

插入數據

QSqlQuery sql_query;
sql_query.prepare("INSERT INTO allfilesdata(filename,filepath,filesize,fileattributes,creat_dwlowtime,creat_dwhightime,lastaccess_dwlowtime,lastaccess_dwhightime,lastwrite_dwlowtime,lastwrite_dwhightime) VALUES(:filename,:filepath,:filesize,:fileattributes,:creat_dwlowtime,:creat_dwhightime,:lastaccess_dwlowtime,:lastaccess_dwhightime,:lastwrite_dwlowtime,:lastwrite_dwhightime)");
sql_query.bindValue(":filename",QString::fromStdWString(fd.cFileName));
sql_query.bindValue(":filepath",QString::fromStdWString(folder));
sql_query.bindValue(":filesize",(int)(fd.nFileSizeHigh*(MAXDWORD + 1) + fd.nFileSizeLow));
sql_query.bindValue(":fileattributes",(int)fd.dwFileAttributes);
sql_query.bindValue(":creat_dwlowtime",(int)fd.ftCreationTime.dwLowDateTime);
sql_query.bindValue(":creat_dwhightime",(int)fd.ftCreationTime.dwHighDateTime);
sql_query.bindValue(":lastaccess_dwlowtime",(int)fd.ftLastAccessTime.dwLowDateTime);
sql_query.bindValue(":lastaccess_dwhightime",(int)fd.ftLastAccessTime.dwHighDateTime);
sql_query.bindValue(":lastwrite_dwlowtime",(int)fd.ftLastWriteTime.dwLowDateTime);
sql_query.bindValue(":lastwrite_dwhightime",(int)fd.ftLastWriteTime.dwHighDateTime);
if(!sql_query.exec())
{
	qDebug() << sql_query.lastError();
}
else
{
    qDebug() << "inserted data successfully!";
}

佔位符

QSqlQuery sql_query;
QString searchstr="select * from allfilesdata where filename LIKE :linetext";
sql_query.prepare(searchstr);
sql_query.bindValue(":linetext",QString("%%1%").arg(linetext));

注意，LIKE子句中使用到的百分號(%)不是在SQL字符串中出現的，而是在綁定佔位符的值的時候出現的，而且LIKE子句在SQL字符串中不能使用單引號(’)，因爲佔位符的類型就是字符串，所以就不需要在LIKE子句中再使用單引號(’)了。

Qt5連接mysql數據庫時報錯

QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QMYSQL QMYSQL3 QODBC QODBC3 QPSQL QPSQL7
QSqlQuery::prepare: database not open

報錯原因1：缺少libmysql.dll
解決辦法：將 MySQL目錄下\MySQL Server 5.5\lib\libmysql.dll複製到項目編譯目錄

報錯原因2：服務器未開啓mysql
解決辦法：systemctr start mysqld.service (centos7)

報錯原因3：服務器未關閉防火牆
解決辦法：systemctr stop firewalld.service (centos7)