数据
-- 学生
create table Student(sid varchar(10),sname varchar(10),sage datetime,ssex nvarchar(10));
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
-- 课程
create table Course(cid varchar(10),cname varchar(10),tid varchar(10));
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');
-- 老师
create table Teacher(tid varchar(10),tname varchar(10));
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');
-- 分数
create table SC(sid varchar(10),cid varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);
01
查询"01"课程比"02"课程成绩高的学生的信息及课程分数
SELECT
*
FROM
(SELECT * FROM SC WHERE cid='01') a
JOIN
(SELECT * FROM SC WHERE cid='02') b on a.sid = b.sid
SELECT
*
FROM
(SELECT * FROM SC WHERE cid='01') a
JOIN
(SELECT * FROM SC WHERE cid='02') b on a.sid = b.sid and a.score > b.score
JOIN
Course c on a.cid = c.cid
JOIN
Course d on b.cid = d.cid
SELECT
*
FROM
(SELECT * FROM SC WHERE cid='01') a
JOIN
(SELECT * FROM SC WHERE cid='02') b on a.sid = b.sid and a.score > b.score
JOIN
Course c on a.cid = c.cid
JOIN
Course d on b.cid = d.cid
JOIN
Student e on a.sid = e.sid
-- 01
SELECT
e.sid,
e.sname,
e.sage,
e.ssex,
a.cid AS cid01,
c.cname AS cname01,
a.score AS cscore01,
b.cid AS cid02,
d.cname AS cname02,
b.score AS cscore02
FROM
( SELECT * FROM SC WHERE cid = '01' ) a
JOIN ( SELECT * FROM SC WHERE cid = '02' ) b ON a.sid = b.sid AND a.score > b.score
JOIN Course c ON a.cid = c.cid
JOIN Course d ON b.cid = d.cid
JOIN Student e ON a.sid = e.sid
02
查询学生选课存在" 01 “课程但可能不存在” 02 "课程的情况(不存在时显示为 null)
SELECT
*
FROM
( SELECT * FROM SC WHERE cid = '01' ) a
LEFT JOIN ( SELECT * FROM SC WHERE cid = '02' ) b ON a.sid = b.sid
03
查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩
SELECT
*,
AVG(score) avg
FROM sc
GROUP BY sc.sid
HAVING avg >= 60
SELECT
a.sid, b.sname, a.avg
FROM
( SELECT *, AVG( score ) avg FROM sc GROUP BY sc.sid HAVING avg >= 60 ) a
JOIN Student b ON a.sid = b.sid