Question

Just for an example. How can I query my db to find two users who might be using the same phone number? I’m not inputting a specific number but I want to find all instances phone numbers that are being used more than once in the user table.

Answer 1

SELECT ... FROM users u1 JOIN users u2 
ON u1.user_id <> u2.user_id AND u1.phone_number = u2.phone_number;