Check for success of $wpdb->update() correctly

My code is

if( $wpdb->update($tableName,array('opt_value'=>$cInfo),array('opt_name'=>'showWeatherWidget')))
    //show success message
else
    // show failure message

This is not correct, $wpdb->update() returns false if it doesn’t change any data, but there were no errors. Can someone tell me the proper way to display a success message that a field was updated?

The correct way is with === FALSE which differentiates from equalling zero, which is what a succesful query with no results returns.

if( $wpdb->update($tableName,array('opt_value'=>$cInfo),array('opt_name'=>'showWeatherWidget')) === FALSE)
    //show failure message
else
    // show success message