sql语句 NULL参与运算（注意事项）

CREATE TEMPORARY TABLE view_table1 SELECT yh_id,SUM(jine) AS jine FROM liushuizhang WHERE lb IN(3,4) GROUP BY yh_id；
CREATE TEMPORARY TABLE view_table2 SELECT yh_id,SUM(jine) AS jine FROM liushuizhang WHERE lb IN(1,2) GROUP BY yh_id；
SELECT yonghu_xinxi.id,if(view_table1.jine IS NULL,0,view_table1.jine)/(if(view_table2.jine IS NULL,0,view_table2.jine) + yonghu_xinxi.jine) AS shuadanlv FROM view_table1 RIGHT JOIN yonghu_xinxi ON yonghu_xinxi.id = view_table1.yh_id LEFT JOIN view_table2 ON yonghu_xinxi.id = view_table2.yh_id；

当a=NULL时，a+任何值都等NULL；
处理办法，如上if（）。