Magento: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '100000001' for key 'UNQ_SALES_FLAT_ORDER_IN

Question

I have installed Magento 1.9.0.1 and I am live since 1 month. The first order of a Client worked without Problem. But now following error message appears when the order should

Answer 1

Try this solution. This would definitely help you.

The order number 100000001 (i.e. increment ID or increment_id) already exists in your order table, sales_flat_order, and it's failing the order save when someone checks out because increment_ids must be unique.

First, verify that you have these order numbers you see in the error messages are indeed already present in the sales_flat_order.increment column. Then, you need to modify the eav_entity_store.increment_id value(s), so that new increment IDs will never overlap with your the already existing order numbers.

Check the maximum value in sales_flat_order.increment_id, and update eav_entity_store.increment_id with a value greater than that.