数据库连接后会显示 QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed. 更换数据表显示 QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work. QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.