This article outlines the database structure for the MMv4 product_instance database table.

• id
  Primary Key of the table.
  int(10) | unsigned | auto increment | primary key | indexed
• pid
  A reference to the product.id field.
  int(10) | unsigned | indexed
• instance_text
  Contains a string that may be used as the product's serial number, license key, etc.
  varchar(255) | indexed
  
• create_date
  The Unix timestamp of the date the database record was created.
  int(10) | unsigned | indexed
  
• order_item_id
  A reference to the order_item.id field.
  int(10) | unsigned | indexed