instruction: a) How many posts were created in 2017?.
response: SELECT AVG(CAST((JULIANDAY(CreationDate) - JULIANDAY(B.postCreationDate)) * 86400.0 AS INT) * 1.0) FROM Posts AS A JOIN (SELECT AcceptedAnswerId, CreationDate AS postCreationDate FROM Posts WHERE NOT AcceptedAnswerId LIKE ' ' AND TIME_TO_STR(CreationDate, '%Y') LIKE '2017') AS B ON A.Id = B.AcceptedAnswerId