How to design a field (type index, restrictions, etc.)?

Question

MySQL

There are such fields as user id and product Id
, they can be in the form of a string and numbers
. And it will often be searched for: i.e. we will have some kind of id (or array) at the input and we will need to find strings among millions
Question: How can I format this field (type, limit, index, etc.) I
use postgres