Need your suggestions on a project's "thinking".

You need a unique PIN (at least 10 digit alpha-numeric value) for each user. It will be stored in the User table (#1).

It is not sufficient to match only the email address before writing information to the Contact_info table. Someone could submit a fictitious set of information if all they need is the email address. I would reject any NEW registration if it uses an email address which is already in your Contact_info table. Only one registration allowed for each email address.

Table #3 is probably some other name than "Users" because that is your name for table #1. Perhaps you meant "Pets" as the name for table #3?

This is how I would configure these three tables

Users
-id unique, auto-increment primary key
-PIN unique

Contact_Info
-user_id link pointing to Users:id
-name encrypted
-email encrypted

Pets
-user_id link pointing to Users:id
-pet_name

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