头疼的问题

1、查询1832班的成绩信息
select chinese,english,math from grade where class=1832;
2，查询1833班，语文成绩大于80小于90的成绩信息
select chinese from grade where class=1833 having chinese>80 and chinese<90;
3，查询学生表中5到10行的数据
select * from grade where sid limit 4,6;
4，显示1832班英语成绩为98，数学成绩为77的姓名与学号，
select name,sid from grade where class=1832 and english=98 and math=77;
5，查询出1832班成绩并且按语文成绩排序(降序)
select * from grade where class=1832 order by chinese desc;
6，查询1833班与1832班，语文成绩与数学成绩都小于80的姓名。
select name,class=1833 or class=1832 from grade where chinese<80 and math<80;
7，查询出没有参加语文考试的学生姓名和班级名称。
select name,class from grade where chinese is null;
8，求出班上语文成绩不及格的学生姓名
select name from grade where chinese<60;
9，求出每个班的数学平均成绩
select class,avg(math) from grade group by class;
10、求出每个班级语文成绩总分--涉及到每个的时候都需要分组
select class,sum(chinese)as c from grade group by class;
11、将语文成绩不及格的学生成绩改为60分
update grade set chinese=60 where chinese<60;
12、三科分数都大于70分的人名和年纪
select name,age from grade where chinese>70 and english>70 and math>70;
13、求出英语分数高于70且其它任何一科目大于60分的人和班级
select name,class from grade where english>70 and (chinese>60 or math>60);
14、统计每个班的人数
select class,count(class) from grade group by class;
15、求每个班数学成绩大于80的人数
select class,count(class) from grade where math>80 group by class;