create table student(
id int,
name varchar(20),
chinese int,
english int,
math int
);
insert into student(id,name,chinese,english,math) values(1, '范真建',80,85,90);
insert into student(id,name,chinese,english,math) values(2,'罗住哪',90,95,95);
insert into student(id,name,chinese,english,math) values(3,'杜子腾',80,96,96);
insert into student(id,name,chinese,english,math) values(4,'范啥冰',81,97,85);
insert into student(id,name,chinese,english,math) values(5,'申晶冰',85,84,90);
insert into student(id,name,chinese,english,math) values(6,'奥丽海',92,85,87);
insert into student(id,name,chinese,english,math) values(7,'郭的辉',75,81,80);
insert into student(id,name,chinese,english,math) values(8,'拎壶尿',77,80,79);
insert into student(id,name,chinese,english,math) values(9,'任他行',95,85,85);
insert into student(id,name,chinese,english,math) values(10,'史真香',94,85,84);
基础SQL

查询表中所有学生的信息。
  select * from student;
查询表中所有学生的姓名和对应的英语成绩。
  select name,english from student;
过滤表中重复数据。
  select english from student;
  select DISTINCT english from student;
  select DISTINCT english,name from student;
  select english+chinese+math from student;
  select english+chinese+math as 总分 from student;
  select name,english+chinese+math as 总分 from student;
在所有学生英语分数上加10分特长分。
  select name,english+10 from student;
统计每个学生的总分。
  select english+chinese+math from student;
使用别名表示学生分数
  select name,english+chinese+math as 总分 from student;
  select name,english+chinese+math 总分 from student;
查询姓名为何东的学生成绩
  select * from student where name='何东';
查询英语成绩大于90分的同学
  select * from student where english>90;
查询总分大于250分的所有同学
  select * from student where english+chinese+math>250;
查询英语分数在 85－95之间的同学。
  select * from student where english>=85 and english<=95;
  select * from student where english between 85 and 95;
查询数学分数为84,90,91的同学。
  select * from student where math=84 or math=90 or math=91;
  select * from student where math in(84,90,91);
查询所有姓何的学生成绩。
  select * from student where name like '何%';
查询数学分>85，语文分>90的同学。
  select * from student where math>85 and chinese>90;
对数学成绩排序后输出。
  select * from student order by math;
对总分排序后输出，然后再按从高到低的顺序输出
  select * from student order by math+chinese+english desc;
对姓何的学生成绩排序输出
  select * from student where name like '何%' order by math+chinese+english desc;
  select name, math+chinese+english from student where name like '何%' order by math+chinese+english desc;
统计一个班级共有多少学生？
  select count(*) from student;
统计数学成绩大于90的学生有多少个？
  select count(*) from student where math>90;
统计总分大于250的人数有多少？
  select count(*) from student where math+chinese+english>250;
统计一个班级数学总成绩？
  select sum(math) from student;
统计一个班级语文、英语、数学各科的总成绩
  select sum(math), sum(chinese), sum(english) from student;
统计一个班级语文、英语、数学的成绩总和
  select sum(math+chinese+english)from student;
  select sum(math)+sum(chinese)+sum(english) from student;
求一个班级数学平均分（avg是MySQL的函数）
  select avg(math) from student;
求一个班级总分平均分
  select avg(math+chinese+english)from student;
  select avg(math)+avg(chinese)+avg(english) from student;
求班级最高分和最低分
  select max(math+chinese+english),min(math+chinese+english) from student;

为学生表，增加一个班级列，练习分组查询。    
  alter table student add column class_id int;    
  注意语法：Oracle中不能有“column”关键字，MySQL中有没有“column”都可以执行。
更新表：
  update student set class_id=1 where id<=5;
  update student set class_id=2 where id>5;
  (update student set class_id=2 where id between 6 and 10;)
查出各个班的总分，最高分。
求各个班级 英语的平均分：
  select classid, avg(english) 
  from student
  group by class_id
如根据组函数的语法要求，将select后增加name列，而不加至group by 之后：
  select name, classid, avg(english)
  from student
  group by classid;
会发现MySQL检查不出错误。相比Oracle数据库，MySQL分组检查不严格。
  select sum(math+chinese+english),max(math+chinese+english) from student group by class_id;
查询出班级总分大于1300分的班级ID
  select class_id from student group by class_id having sum(math+chinese+english)>1300;
  select class_id from student where sum(math+chinese+english)>1300 group by class_id ;
对于组函数的应用与Oracle类似，可以应用于Having中，但不能用于where子句中。