I have added a custom field to my create account page for a referral code. The field is manditory and produces an appropriate message. I also have a table in the database that I will store referral codes. I need the create account page to check and see if the referral code is correct based on the information stored in the db table.
Any help would be appreciated.

1. Click on Configuration > Customer Details to access the common Customer Details screen.

At the bottom of this page, you'll see 'Customers Referral Status', edit it.

**Customers Referral Code is created from
0= Off
1= 1st Discount Coupon Code used
2= Customer can add during create account or edit if blank

NOTE: Once the Customers Referral Code has been set it can only be changed in the Admin Customer**

When new user create account, it will submit its referral code to 'create_account.php' which is under '\includes\modules' folder. In the create_account.php file, you can query one of your tables which stores the defined referral code to match the $_POST['customers_referral'], and validate it.