Friend Requests Acceptance Rate

Problem

Schemas: FriendRequest(sender_id INT, receiver_id INT, request_date DATE) and RequestAccepted(requester_id INT, accepter_id INT, accept_date DATE). Return the overall acceptance rate: distinct accepted pairs ÷ distinct requested pairs, rounded to 2 decimals. If there are no requests, return 0.

Constraints

• (sender, receiver) may repeat; count distinct.

Approach — Core Patterns

This is a Core Patterns problem. The idea: pick the data structure best matched to the constraints and solve it in one clean pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: see the walkthrough below.

Solution code

SQL

SELECT ROUND(
  COALESCE(
    (SELECT COUNT(*) FROM (SELECT DISTINCT requester_id, accepter_id FROM RequestAccepted)) * 1.0
    / NULLIF((SELECT COUNT(*) FROM (SELECT DISTINCT sender_id, receiver_id FROM FriendRequest)), 0),
    0
  ), 2
) AS acceptance_rate;

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.