instruction: Percentage of Questions with the Accepted Answer @until.
response: SELECT (CAST(COUNT(DISTINCT q.Id) AS FLOAT) / (SELECT COUNT(*) FROM Posts WHERE Posts.CreationDate < @until AND PostTypeId = 1) * 100) AS AcceptedPercentage FROM Posts AS q INNER JOIN Posts AS a ON q.Id = a.ParentId WHERE a.PostTypeId = 2 AND q.CreationDate < @until AND q.PostTypeId = 1