WITH
Request AS (
SELECT COUNT(DISTINCT sender_id, send_to_id) AS `count`
FROM FriendRequest
),
Accepted AS (
SELECT IFNULL(COUNT(DISTINCT requester_id, accepter_id), 0) AS `count`
FROM RequestAccepted
)
SELECT IF(
`Request`.count = 0,
0,
ROUND(Accepted.`count` / Request.`count`, 2)
) AS accept_rate
FROM Request, Accepted;