获取当月总天数+上(几个月)月天数之和
SELECT
	(
		DATEDIFF(
			date_add(
				curdate() - DAY (curdate()) + 1,
				INTERVAL 1 MONTH
			),
			DATE_ADD(
				curdate(),
				INTERVAL - DAY (curdate()) + 1 DAY
			)
		)
	) +(
		DATEDIFF(	
			DATE_ADD(
				curdate(),
				INTERVAL - DAY (curdate()) + 1 DAY
			),
			date_add(
				curdate() - DAY (curdate()) + 1,
				INTERVAL - 你要往前推几个月 MONTH
			)
		)
	)
FROM
	DUAL
原文:https://www.cnblogs.com/Darkqueen/p/8867068.html