MYSQL中IFNULL的使用 以及统计2张表的字段和

SELECT SUM(total) as guess_right from (
	select 
		IFNULL(ff_soccer_prize_knockout.guess_right_champion, 0) + 
		IFNULL(ff_soccer_prize_knockout.guess_right_strong8, 0) +
		IFNULL(ff_soccer_prize_knockout.guess_right_strong4, 0) + 
		IFNULL(ff_soccer_prize_knockout.guess_right_strong2, 0) as total
	from 
		ff_soccer_prize_knockout 
	where 
		playerid = "292578082"
	
	UNION ALL

	select 
			sum(guess_right) total from ff_soccer_prize 
	where 
		ff_soccer_prize.playerid = "292578082"
	GROUP BY ff_soccer_prize.playerid
) c

IFNULL 当第一个字段值为NULL时默认给它设置为0，将4个字段的值统计和 。然后将第一个表的数据和第二个表的数据进行统计，两张表设置的字段都为total

IFNULL为MYSQL的函数