How to avoid duplicates?

Question

MySQL

There are several columns, number (number) and tag (category). How to compose an INSERT so that number cannot be subscribed to tag multiple times?
(Not allowed:
NUMBER | TAG
[phone]
[phone]
[phone]
Allowed:
[phone]
[phone]
[phone])

Answer 1

Immediately initialize the base for all numbers, and change only the value?

Answer 2

Set up pg_hba.conf, create users, give permissions, etc.
https://wiki.postgresql.org/wiki/Client_Authentication
https://www.postgresql.org/docs/9.6/static/auth-me...