-- 同学持有的手机记录表
create table student_phone (
id int primary key,
stu_name varchar2(20),
phone varchar2(200)
)
insert into student_phone values (1,\'小红\',\'华为 荣耀v9\');
insert into student_phone values (2,\'小军\',\'荣耀v9(华为)\');
insert into student_phone values (3,\'小红\',\'小米note2\');
insert into student_phone values (4,\'小平\',\'小米 note2\');
insert into student_phone values (5,\'小平\',\'小米 note2\');
insert into student_phone values (6,\'小云\',\'小米 Note2\');
insert into student_phone values (7,\'小云\',\'小米 NOTE2\');
insert into student_phone values (8,\'小云\',\'小米 NOTE 2\');
commit
select phone,count(1) t from student_phone
group by phone order by t desc
---------------------------
drop table student_phone
create table student_phone (
id int primary key,
stu_name varchar2(20),
phone int
)
create table phone(
id int primary key,
phone_name varchar2(200)
)
insert into phone values(1,\'荣耀v9(华为)\');
insert into phone values(2,\'小米 note2\');
commit
select * from phone
select * from student_phone
insert into student_phone values (1,\'小红\',1);
insert into student_phone values (2,\'小军\',1);
insert into student_phone values (3,\'小红\',2);
insert into student_phone values (4,\'小平\',2);
insert into student_phone values (5,\'小平\',2);
insert into student_phone values (6,\'小云\',2);
insert into student_phone values (7,\'小云\',2);
insert into student_phone values (8,\'小云\',2);
commit
select phone,count(1) t from student_phone
group by phone order by t desc
可以通过phone=id
select * from student_phone,phone
where student_phone.phone=phone.id
------------------------------
select a.stu_name,b.phone_name from student_phone a,phone b
where a.phone=b.id
-------------------------------------
select phone_name,count(1) 总人数 from
(
select a.stu_name,b.phone_name from student_phone a,phone b
where a.phone=b.id
) ttttt
group by phone_name order by 总人数 desc
----------------------------
-- 多表关联
-- 内关联跟左关联只是改一下关键字inner—>left
-- 内关联
select * from student_phone,phone
where student_phone.phone=phone.id
-- 1.内关联 (丢失不满足的记录条数)
select * from student_phone a
inner join
phone b on a.phone=b.id
--
insert into student_phone values (9,\'小成\',3);
commit
select * from phone
select * from student_phone
select a.stu_name,b.phone_name from student_phone a
inner join
phone b on a.phone=b.id
--测试
insert into phone values(3,\'iphone8（美国总统专用）\');
commit
delete from phone where id=3
丢失了小成
-- 2.左关联
select a.stu_name,b.phone_name from student_phone a
left join
phone b on a.phone=b.id
-- 改进一下
select a.stu_name,nvl(b.phone_name,\'未知\') from student_phone a
left join
phone b on a.phone=b.id
--回归原始 (oracle专用+：即把丢失的+回来)
select a.stu_name,b.phone_name from student_phone a,phone b
where a.phone=b.id(+)
--求什么手机最多人使用（排序）
--分组[后]最大值
select * from(
select phone,count(1) counts from student_phone group by phone
order by counts desc
)
where rownum=1
select * from(
select phone,count(1) counts from student_phone group by phone
order by counts asc
)
where rownum=1