数据库操作命令

...

create table stu(

id int unsigned not null auto_increment primary key,

name varchar(8) not null unique,

age tinyint unsigned,

mysql> alter table tt modify age tinyint unsigned not null default 20;

mysql> alter table tt change name username varchar(16);

Query OK, 0 rows affected (0.11 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> insert into stu values(null,'wangwu',25,'w','python03');

mysql> select *,age+5 age5 from stu;

mysql> select *,'shanghai' city from stu;

mysql> select concat(classid,":",name) from stu;

mysql> select * from stu where classid is null;

max() min() sum() avg() count()

select max(age),min(age),sum(age),avg(age),count(id) from stu;

select sex,count(*) from stu group by sex;

mysql> select classid,count(*) from stu where classid is not null group by classid;

select classid,sex,count(*) from stu where classid is not null group by classid,sex;