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--median
select median(score) from student;
select classno,median(score) score from student group by classno;
?案例1--学生选课
1. 创建表 stu（学生表），course（课程表），选课表（s_c）
--创建表
create table STU
(
id NUMBER not null,
name VARCHAR2(255)
) ;
create table COURSE
(
id NUMBER not null,
coursename VARCHAR2(255)
) ;
create table S_C
(
sid NUMBER,
cid NUMBER,
score NUMBER
);
2.插入数据
--插入数据
Insert into STU (ID,NAME) values (1,‘wish‘);
Insert into STU (ID,NAME) values (2,‘rain‘);
Insert into STU (ID,NAME) values (3,‘july‘);
Insert into STU (ID,NAME) values (4,‘joey‘);
Insert into COURSE (ID,COURSENAME) values (1,‘math‘);
Insert into COURSE (ID,COURSENAME) values (2,‘english‘);
Insert into COURSE (ID,COURSENAME) values (3,‘Japanese‘);
Insert into COURSE (ID,COURSENAME) values (4,‘chinese‘);
Insert into S_C (SID,CID,SCORE) values (1,80);
Insert into S_C (SID,2,90);
Insert into S_C (SID,SCORE) values (2,4,100);
Insert into S_C (SID,SCORE) values (4,SCORE) values (3,60);
3.查询学生选课情况
with vt as
(select s.id,s.name,c.coursename,sc.score from stu s,course c,s_c sc where s.id=sc.sid and c.id=sc.cid)
select * from vt order by id;
结果：
?
案例2--图书馆借阅
1.创建表： 图书（book），读者（reader），借阅（borrow）
--创建表 book
create table book(
bookId varchar2(30),--图书总编号
sortid varchar2(30),--分类号
bookname varchar2(100),--书名
author varchar2(30),--作者
publisher varchar2(100),--出版单位
price number(6,2) --价格
);
--创建表 reader
create table reader (
cardId varchar2(30),--借书证号
org varchar2(100),--单位
name varchar2(100),--姓名
gender varchar2(2),--性别
title varchar2(30),--职称
address varchar2(100) --地址
);
--创建表 borrow
create table borrow(
cardId varchar2(30),--借书证号
bookId varchar2(30),--图书总编号
borrowDate varchar2(30) --借阅时间
);
2.插入数据
--插入数据-book
insert into book (bookId,sortid,bookname,author,publisher,price)
values (‘aaa‘,‘a1‘,‘gone with the wind‘,‘CA‘,‘renmin‘,‘103‘);
insert into book (bookId,price)
values (‘bbb‘,‘a2‘,‘the little prince‘,‘CB‘,‘jixie‘,‘30‘);
insert into book (bookId,price)
values (‘ccc‘,‘a3‘,‘the ordinary world‘,‘CC‘,‘130‘);
insert into book (bookId,price)
values (‘ddd‘,‘a4‘,‘the little women‘,‘dianzi‘,‘110‘);
--插入数据-reader
insert into reader(cardid,org,name,gender,title,address)
values (‘xxx‘,‘A‘,‘wish‘,‘student‘,‘bupt‘);
insert into reader(cardid,address)
values (‘uuu‘,‘luna‘,address)
values (‘vvv‘,‘B‘,‘harry‘,address)
values (‘www‘,‘C‘,‘chander‘,‘2‘,‘professor‘,address)
values (‘yyy‘,‘joey‘,address)
values (‘zzz‘,‘richard‘,address)
values (‘OOO‘,‘micheal‘,address)
values (‘ppp‘,‘richal‘,address)
values (‘abp‘,‘michal‘,address)
values (‘ccp‘,‘mike‘,‘bupt‘);
--插入数据-borrow
insert into borrow(cardid,bookid,borrowdate) values(‘xxx‘,‘aaa‘,‘2014-4-29‘);
insert into borrow(cardid,‘bbb‘,‘ccc‘,‘2014-4-28‘);
insert into borrow(cardid,borrowdate) values(‘yyy‘,‘ddd‘,‘2014-4-27‘);
insert into borrow(cardid,borrowdate) values(‘zzz‘,borrowdate) values(‘uuu‘,‘2014-4-26‘);
insert into borrow(cardid,borrowdate) values(‘vvv‘,borrowdate) values(‘www‘,‘2014-4-26‘);
表信息如下：
book------> reader-------> borrow
?
?
?
3. 查询A单位借阅图书的读者人数和人员详细信息
人数：
with vt1 as
(select cardid from reader where reader.org=‘A‘)
select count(1) from vt1 where exists (select cardid from borrow where borrow.cardid=vt1.cardid);
详细信息：
with vt1 as
(select cardid,org from reader where reader.org=‘A‘)
select cardid,org from vt1 where exists (select cardid from borrow where borrow.cardid=vt1.cardid);
4.查询借书证号尾字符为‘p‘的读者
select cardid,org from reader where cardid like ‘%p‘;
5.?查询名字以m开头的女性读者，‘1’显示为女，‘2’显示为男
select cardid,
case when gender=‘1‘ then ‘女‘ when gender=‘2‘ then ‘男‘ else ‘其他‘ end gender
from reader where name like ‘m%‘;
6.?2014年2-4月借过书的读者
1)查询满足条件的读者（仅包含cardid）--未去重
方式一：
select cardid,borrowdate from borrow where to_char(to_date(borrowdate,‘yyyy-mm-dd‘),‘yyyy‘)=‘2014‘
and to_char(to_date(borrowdate,‘mm‘)>=‘02‘
and to_char(to_date(borrowdate,‘mm‘)<=‘04‘;
方式二：
select cardid,‘yyyy‘)=‘2014‘ --查询
and to_char(to_date(borrowdate,‘yyyy-mm‘)>=‘2014-02‘
and to_char(to_date(borrowdate,‘yyyy-mm‘)<=‘2014-04‘;
方式三：
select cardid,‘yyyy-mm-dd hh24:mi:ss‘);
2) 查询+去重
select distinct cardid from borrow where to_char(to_date(borrowdate,‘yyyy‘)=‘2014‘ --查询+去重
and to_char(to_date(borrowdate,‘yyyy-mm‘)<=‘2014-04‘;
select distinct cardid from borrow where to_date(borrowdate,‘yyyy-mm-dd hh24:mi:ss‘);
3）查询+去重+读者姓名等信息
with vt1 as (select distinct cardid from borrow where to_char(to_date(borrowdate,‘yyyy‘)=‘2014‘ and to_char(to_date(borrowdate,‘yyyy-mm‘)>=‘2014-02‘and to_char(to_date(borrowdate,‘yyyy-mm‘)<=‘2014-04‘)select cardid,org from reader where exists (select cardid from vt1 where vt1.cardid=reader.cardid);
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