When all the data has been fetched from a SELECT statement, the driver should automatically call finish for you. So you should not normally need to call it explicitly except when you know that you've not fetched all the data from a statement handle. The most common example is when you only want to fetch one row, but in that case the selectrow_* methods may be better anyway. Adding calls to finish after each fetch loop is a common mistake, don't do it, it can mask genuine problems like uncaught fetch errors.