how to connect to a slot when a row is selected in TableView?

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I'm pretty sure that the

connect(view->selectionModel(),SIGNAL(currentRowChanged(QModelIndex,QModelIndex)),this,SLOT(querydb()));

connect(view->selectionModel(),SIGNAL(currentRowChanged(QModelIndex,QModelIndex)),this,SLOT(querydb()));

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will not work since your signal and your slot don't have the same parameters type. When you connect, you have to connect a signal to a slot with exactly the same parameters.

Hope this helps.