instruction: Reputation of users with 1 question.
response: WITH singlePostUsers AS (SELECT OwnerUserId FROM Posts AS p GROUP BY OwnerUserId HAVING COUNT(Id) = 1) SELECT AVG(Reputation) AS average_rep, SUM(CASE WHEN Reputation < 15 THEN 1 ELSE 0 END) AS Under15, SUM(CASE WHEN Reputation < 15 THEN 0 ELSE 1 END) AS Over15 FROM singlePostUsers AS spu INNER JOIN Posts AS p ON spu.OwnerUserId = p.OwnerUserId INNER JOIN Users AS u ON spu.OwnerUserId = u.Id WHERE PostTypeId = 1