I have created a dev site with the newest version 1.9.1 of magento & created a new database for the dev site & copied the old database over to the new, all good so far.
Whilst working on the new site, the old site was/is still live & taking new orders & now has come time to make the new site live so first I need to move the customers & orders to the new database.
Magento backend & Export customer from old site & via backend of new site Import, all good happy days.
No way that I can se to export sales from Magento backend so into phpMyAdmin & export all tables starting sales_ but when I try to import into the new database it throws a error:
1452 - Cannot add or update a child row: a foreign key constraint fails ('admin_ma9poster'.'sales_flat_invoice', CONSTRAINT 'FK_SALES_FLAT_ORDER_ID_SALES_FLAT_ORDER_ENTITY_ID' FOREIGN KEY ('order_id') REFERENCES 'sales_flat_order' (entity_id') ON DELETE CA)
I have tried emptying the tables before import, deleting the tables before import, exporting in different formats but all lead to different sorts of errors.
Am I going about this the right way or is there a module that might do this for me.
The way you followed for upgrade is not prorper, because database structure of Magento 1.8 and 1.9 is different, it will not be upgraded simply by copy pasting tables.
For your requirement, you can use this extensions : https://www.magecomp.com/magento-order-import-export.html
If moving manually is difficult for you, you should look for a help to move properly. You should be careful of your data.
I read magento upgrade guide to move data from magento 1.8 to 1.9. It is not complicated. You can try it.