drop column birthday;

3.清空表中的数据(与delete from table_name区分开) truncate table emp2;

4.重命名表 rename emp2 to emp3;

5.删除表

drop table emp3;

数据处理 DML

1）增

1.1 增添一条记录

insert into [表名](,,,,,)

values(,,,,,)

1.2 从其它表中拷贝数据

insert into [表名]

select .... from [另一个表]

where ....

2）改

update [表名]

set .....

where ....

3）删

delete from [表名]

where ....

4）查(最常用的数据库操作)

select ....

from …

where ….

group by …

having …

order by ….

约 束

对创建的表的列属性、字段进行的限制。诸如:not null/unique/primary key/foreign key/check