题解 | #月总刷题数和日均刷题数#

```WITH t AS (
	SELECT
		*,
		DAY ( LAST_DAY( submit_time ) ) days,
		DATE_FORMAT( submit_time, "%Y%m" ) submit_month 
	FROM
		practice_record 
	WHERE
		YEAR ( submit_time ) = "2021" 
	) SELECT
	submit_month,
	count( question_id ) month_q_cnt,
	ROUND( count( question_id ) / days, 3 ) avg_day_q_cnt 
FROM
	t 
GROUP BY
	submit_month,
	days UNION ALL
SELECT
	"2021汇总" AS submit_month,
	count( question_id ) month_q_cnt,
	ROUND( count( question_id ) / 31, 3 ) avg_day_q_cnt 
FROM
	t
ORDER BY
	submit_month ASC