Hello all, first post here. Just a small suggestion as i've run across a quite fatal problem merging two existing zen cart installs.

Here's the problem, when merging two existing zen cart installs with active customers you will run into the problem of customers_default_address_id being duplicated which if i knew about it before doing the import and before losing one of the databases would not have been a huge deal to work around. But i found out afterwards when customers info was not showing up on orders.php in the admin.

My suggestions to alleviate this problem:
a) be aware of it before merging and write your import scripts in a way that updates this field as the import is happening.

b) remove customers_default_address_id from the customers table and add a column in the address book `default` tiny int 0 or 1 this way as long as the customer id is updated to match the auto_incremented customer_id in the customers table the address_book table should still agree with the customers table.

c) you're like me and it's too late to change what is done, I'm in the process of writing a few querys to find customers who have a default_address_id that doesn't exist in the address_book table and to update their id to be the first one found that their customer_id is linked to. A work around - but better than seeing empty customer fields in an invoice.

any suggestions or prior solutions appreciated. still i will try to share my solution for merging two zen cart installs as I get deeper into it.