1.DDL
1.创建表
create table if not exists t_student(id integer auto_increment primary key ,name
varchar(3) , age int);
- 删除表
drop table if exists t_student;
- 修改表结构
alter table t_student add address varchar(4);
alter table t_student modify address varchar(6) not null;
tip：
简单约束：
name varchar(3) not null
age int default 66
主键约束：
id integer auto_increment primary key
2. DML
1.插入数据
insert into t_student(name,age,address) values ('xiaoM',12,'guangzhou');
2.修改数据
update t_student set name='xiaoHuang' where id=1;
3.删除数据
delete from t_student where id= 1 ;
tip：
条件约束
delete from t_student where id is 1 or name = 'xiaoM';
3. DQL
查询语句
1.查询所有字段信息
select * from t_student;
2.查询部分字段信息
select name,age from t_student;
3.查询符合条件下的部分字段信息
select name,age from t_student where id=2;
4.查询数据个数
select count(*) from t_student;
5.查询age不为空值的个数
select count(age) from t_student;
6.查询age平均值
select avg(age) from t_student;
7.查询age总和
select sum(age) from t_student;
8.查询age最大值
select max(age) from t_student;
9.查询age最小值
select min(age) from t_student;
10.查询按分数升序，按年龄降序
select *from t_student order by score asc, age desc;
