mysql 查询数据为空如何设置默认值

Question

如何把查询出来的null 默认为0;

SQL是:select name,sum(score) as cou from student left join score on (student.id=score.stu_id) group by stu_id order by cou desc;

求指导

Answer 1

select name,sum(if(score is null,0,score)) as cou from student left join score on (student.id=score.stu_id) group by stu_id order by cou desc;

试一下这个

Answer 2

综合一楼和一楼评论，应该用在sum累加score的值前，使用ifnull(expr1,0)判断score列值是否为空，为空则以0计算

select name,sum(ifnull(score,0)) as cou from student left join score on (student.id=score.stu_id) group by stu_id order by cou desc;