有flag的时候计算

假设flag=1的积分是正，flag=0的积分是负数，已知number求总积分

SELECT
	sum_flag_1 - sum_flag_0 AS total
FROM
	(
		(
			SELECT
				sum(point) AS sum_flag_1
			FROM
				points
			WHERE
				flag = 1
			AND number = 10001
		) s1,
		(
			SELECT
				sum(point) AS sum_flag_0
			FROM
				points
			WHERE
				flag = 0
			AND number = 10001
		) s2
	)