Taguchi uses one or more of the following keys (a.k.a. fields and columns), arranged from higher to lower precedence, from an import file to identify subscribers in the database.

• External ID
• Email
• Phone

If a subscriber in the database is found, Taguchi updates the subscriber with associated data in the import file. Otherwise, a new subscriber is created using those data. The rules governing whether to create or update a subscriber can generally be classified by the number of keys used in the import process.

1-Key Identification

 key         | found  | not found
-------------|--------|-----------
 External ID | update | create
 Email       | update | create
 Phone       | update | create

2-Key Identification

 1st/2nd key       | 1st key found | 1st key not found | 2nd key found                                | 2nd key not found
-------------------|---------------|-------------------|----------------------------------------------|-------------------
 External ID/Email | update        | use Email as key  | update if External ID is null else not found | create
 External ID/Phone | update        | use Phone as key  | update if External ID is null else not found | create
 Email/Phone       | update        | use Phone as key  | update if Email is null else not found       | create

For example, if the database currently holds:

 External ID | Email       | Name
-------------|-------------|------
             | a@email.com | John

After importing with (External ID=001, Email=a@email.com, Name=Johny), the database will hold:

 External ID | Email       | Name
-------------|-------------|-------
             | a@email.com | Johny

This is because External ID 001 is not found, and the External ID of the found record (by Email=a@email.com) is null.