复习一下几条简单的mysql语句：

复习一下几条简单的mysql语句：
已知tablename表的数据为：
tablename（id，name,age）
1.查找出表tablename的的id的值大于4的所有字段来
slect * from table_neme where id>4
2.插入到表tablename中值
insert into tablename(id,name,age) value(1,"dyh",23)
3.将id大于4的字段将age字段改为33
update tablename set age=33 where id>4
4查找出name字段中带有dyh的所有字段来
select * from tablename where name like '%dyh%'
5按age的顺序进行排序
select * from tablename order by age
6.求出这张表的总数来
select count(*) as countvalue from tablename
7求出这个age的总和来
select sum(age) as sumvalue fromtablename
8.求出这张表的平均年龄
select avg(age) as avgage from tablename
9求出这张表的最大年龄来
select max(age) maxage from tablename
10求出最小年龄来
select min(age) minage from tablename
delete from tablename where id=0;//删除整行
alter table student add cla_name varchar(14);//添加一个字段
alter table student drop column sum;//删除一个字段
select class.name from class,student where class.cla_name=student.cla_name;//表和表连接