1、数据库:person
创建 create databases person;
查看 show databases;
指定使用 use person;
删除 drop databases person;
2、表:person
creat table person(
列名1 数据类型描述,
列名2 数据类型描述,
列名3 数据类型描述,
列名4 数据类型描述,
);
creat table person(
id int unsigned not null auto_increment primary key,
name char(10) not null,
age tinyint not null,
sex varchar(5) not null,
tel char(13) null default "-"
);
[unsigned 无符号, not null 非空, auto_increment 递增, primary key 主键]
显示表:show tables;
查看表结构:
describe person ;
或者 show columns from/ in person;
根据旧表创建新表
create table student like person;
create table student as select id,name from person;
复制整个表
create table student as select * from person;
[as 可以省略]
删除表:
drop table person;
重新命名表:
rename table person to person1
或者
alter table person rename person1
表名:person
字段:id,name,age
1 张三 20
2 李四 22
3 王五 23
查询:
select id,name,age from person;
select * from person
select id from person where name="李四"
selext id from person where name like "%王%" 名字中带有王字的id
select name from person where age is null
select name from person where id>=2 order by desc 降序
select name from person where id>=2 默认升序
select name from person where id>=2 order by asc 升序
select top 2 name from person mysql显示name的前二行
select * from person where rownum < 2 oracle 显示name的前二行
select name '成都' as 地址 from person 查询name列 添加地址列 值为成都
select name as 姓名 from person where id=2 选出表中id为2的行,显示name列,并将name列改为姓名显示
删除:delete from person where id=1;
修改:update person set name="刘德华" where id=2;
增加:insert into person(id,name,age) values(4,'刘能',24);
或者不要列名,按表定义的顺序填写
insert into person values(4,'刘能',24);
另外一张表:
student
insert into student(id,name,age) select id,name,age from person
删除整个表的数据
truncate table person
添加列:
表的最后添加
alter table person add sex char(3) not null;
在指定的列后面添加:
alter table person add address cha(5) after age;
在表的最前面添加
alter table person add address cha(5) first;
修改列的列名:
alter table person change address address1 char(10) null default "-";
修改列的数字类型:
alter table person change name name char(20) not null;
删除列:
删除表person 中sex列;
alter table person drop sex;
求某列数据总数(不包含缺省)
select count(age) as totalcount from person;
统计表的总行数:
select conut(*) as totalcount from person;
求某列数据的总和;
select sum(id) as idsum from person;
求某列数据的平均值;
select avg(age) as ageavg from person;
求某列数据的最大最小值:
slect max(age) as maxage from person;
slect min(age) as minage from person;