SQL的面试题目，不知道怎么写

Question

所有信息都在图片上了，查找多方无果，希望各位来帮帮我，这个不会啊

Answer 1

1、select ifnull(score,0) from students_grade;

2、
select 
when score between 90 and 100 then '优秀'
when score between 80 and 89 then '良好'
when score between 60 and 79 then '一般'
when score between 0 and 60 then '不及格'
else '缺考'
end 
from students_grade;