It is only warning. Your table has so many columns (or so big columns) that it si possible you will not be able to store all data by INSERT statement. You can accept this possible danger if you are sure that your INSERT statements never exceed this limitation but can you really? You can avoid this warning by redesign the table. Row size check is done with column definition changes and that is why you have seen this warning when deleting column too. That means you already had this situation before trying to delete column.