创建student表，内容如下：
select * from student;
在所有学生数学分数上加10分特长分。
select name,english+10 as english from student;
统计每个学生的总分。
select (chinese+english+math) as '总分' from student;
使用别名表示学生分数
select name as '姓名',chinese,english,math from student;
统计平均分
select name,(chinese+english+math)/3 from student;
查询姓名为ww的学生成绩
select * from student where name='ww';
查询英语成绩大于75的同学
select * from student where english>=75;
查询总分大于220的同学
select * from student where (chinese+english+math)>=220;
查询英语分数在 70－75之间的同学。
select * from student where english BETWEEN 70 and 75;
select * from student where english>=70 and english<=75;
查询数学分数为83,84,85的同学。
select * from student where math in(83,84,85);
查询所有姓李的学生成绩。
select * from student where name like 'li%';
查询数学分>82并且语文分>64的同学。
select * from student where math>82 and chinese>64;
对数学成绩排序后输出(如果不写排序规则，则默认按升序排序)
asc:升序，desc：降序
select * from student order by math;
select * from student order by math asc;
select * from student order by math desc;
指定多个字段进行排序:先按第一个字段排序，如果相同则按第二个字段排序
select * from student order by math asc , chinese desc;
对总分排序后输出，再按从高到低的顺序输出。
select name as 姓名,(chinese+english+math) as 总分 from student order by 总分 desc;
对姓l的学生成绩排序输出
select *,(chinese+english+math) as total from student where name like 'l%' order by total desc;
显示student表格中的前三行
select * from student limit 3;
显示表格中的3-5行(第一个值表示偏移的行数，第二个表示显示的总行数)
select * from student limit 2,3
