题解 | #商品交易(网易校招笔试真题)#

```SELECT LEFT
	( answer_date, 10 ) answer_date,
	ROUND( COUNT( issue_id ) / COUNT( DISTINCT author_id ), 2 ) per_num 
FROM
	answer_tb 
GROUP BY
	LEFT ( answer_date, 10 ) 
HAVING
	SUBSTRING( answer_date, 6, 2 ) = "11" 
ORDER BY
	answer_date ASC