计算每个班的语文总成绩和数学总成绩，要求科目中低于60分的成绩不记录总成绩。
tb_score结构数据：
| name | chinese | maths |
|---|---|---|
| A | 89 | 98 |
| B | 99 | 89 |
| C | 55 | 66 |
| D | 88 | 66 |
| E | 55 | 66 |
| F | 88 | 99 |
tb_class表结构数据：
| stuname | classname |
|---|---|
| A | C1 |
| B | C2 |
| C | C3 |
| D | C2 |
| E | C1 |
| F | C3 |
参考代码
select classname,sum(if(chinese<60,0,chinese)) as chinese,
sum(if(maths<60,0,maths)) as maths
from tb_score s,tb_class c
where s.name=c.stuname
group by classname;