QSqlQuery lastInsertId()

[CodeFreaks]

Hi everyone,
I tried to get last id through QSqlQuery::lastInsertId().

    QSqlDatabase myDb = QSqlDatabase::addDatabase("QMYSQL");
    myDb.setHostName    ("localhost");
    myDb.setUserName    ("root");
    myDb.setPassword    ("");
    myDb.setDatabaseName("testdatabase");

    qDebug()<<"Started!";

    if(myDb.open()){
        qDebug()<<"Database Connected!";
    }else{
        qDebug()<<myDb.lastError();
    }

    bool avFeature = myDb.driver()->hasFeature(QSqlDriver::LastInsertId);
    qDebug()<<"LastInsertedId is availabe: " << avFeature;

    QSqlQuery myQuery(myDb);
    if (myQuery.exec("SELECT id FROM users"))
    qDebug()<<"Last ID: "<<myQuery.lastInsertId();

Output:

Started!
Database Connected!
LastInsertedId is availabe:  true
Last ID:  QVariant(Invalid)

Database:

[JonB]

@CodeFreaks said in QSqlQuery lastInsertId():

QSqlQuery::lastInsertId()

gives you the ID from the last row inserted via an INSERT statement immediately preceding on that QSqlQuery (so that you can tell which row it just inserted). I don't know what you think you're trying to do here, but since you do no INSERT you'll not get any valid value back.

P.S. Do you want to know the highest id column value currently in that table? Then just myQuery.exec("SELECT MAX(id) FROM users") returns it.

[CodeFreaks]

@JonB
Thanks for reply.
I want to get the maximum (last) allocated id within a specific table in the database, as a variable.

[JonB]

@CodeFreaks
So that's what my "P.S." guess above gave you....

[CodeFreaks]

@JonB
I don't know that what's wrong.

    if (myQuery.exec("SELECT MAX(id) FROM users"))
    qDebug()<<"Last ID: "<<myQuery.value(0);

Output:

Database Connected!
LastInsertedId is availabe:  true
Last ID:  QVariant(Invalid)

[Christian Ehrlicher]

@CodeFreaks said in QSqlQuery lastInsertId():

I don't know that what's wrong.

You forgot to retrieve the data with .next() - see http://doc.qt.io/qt-5/qsqlquery.html#details

[CodeFreaks]

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