@Aioria
First let's deal with the use of binding variables. The fact that the examples only tend to show it being used with INSERT is not relevant. They can be used with any SQL statement, be that SELECT, INSERT, UPDATE, DELETE or whatever, so long as you go prepare(), then bindValue(), then exec(). It's just a neater way of getting a variable safely into the statement in the right format in the right place than putting it directly into the string via something like QString::number().
Now your issue. It's not your fault, but I/we find the description of what you are trying to achieve difficult to follow. From the way you want your exec() to be inside the for loop, I now have a feeling you want (potentially) multiple rows to each be updated separately. Does the following describe your situation:
You have some existing rows in the SQL table.
Each row has an id, and a faults counter of its own.
When you go through the checkboxes: if a given row's checkbox is unchecked, you want just that row's faults column to be incremented by 1.
For example:
Row number 2 currently has the value 5 stored in its faults in the database. The teacher does not check its checkbox. So that means you want that row's faults to be incremented to 6.
Meanwhile, another row with value 0 also has its checkbox unchecked, so that row wants it incremented to 1.
And a third row has its checkbox checked, so you do not want that row's faults incremented at all.
Is that it?
In this case, the secret is that you can write your SQL query so that the database side does the incrementing for you, using whatever faults value a given row (specified by id) has currently to add to. Your Qt client does not need to know the number of faults already there. Something like:
for (int i = 0; i < rowCount; i++)
{
if (ui->listWidget->item(i)->checkState() == Qt::Unchecked)
{
QSqlQuery update;
update.prepare("UPDATE students SET faults = faults + 1 WHERE id = :id");
update.bindValue(":id", i);
update.exec()
}
}
