The error “UNQ_SALES_FLAT_ORDER_INCREMENT_ID” is usually seen when magento uses alphanumeric order numbers. When the old customer buys a product again, magento instead of increasing the ordre increment from the latest order, increases the increment from the last order of the same old customer. This creates a duplicate entry and magento refuses to take an order.
You can also receive an email containing “SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry ‘AB100082765’ for key ‘UNQ_SALES_FLAT_ORDER_INCREMENT_ID‘” error or “There was an error processing your request” during placing [...]
As you have by now set your own magento store and you see that the order number a customer gets after purchasing starts from 100000001. But as its your new store and you don’t want your store to look like an amateur to others, you thought of changing the value of the order/shipment/invoice/credit memo number. But as you might have found out that there is no option in magento to change the value of this. Also it occurred to you that you want to modify in a way that it has a prefix related to your store name. e.g. Your store name is BestBooks.com, so you want that your order number looks like BB10023123. It looks definitely better than the default.
So [...]
