message confirmation

TABLE1: SMS_SEND

ds|country|carrier|phone_number|type (type could be confirmation, engagement, etc)

Q1. find the number of unique phone number for each carrier and country

another table: confirmation

ds|contact_point (can be phone number or email)

Q2. the glocal confirmation rate has dropped, and FB thinks it could because of some carriers did not send out SMS confirmation message. What metric would you use to evaluate it? code it

follow-up (combined with some coding):

how to prioritize what top 10 countries to solve this issue? (after some explaination, the interviewer asked me to use the previous two tables to find an answer...)