SQL语句多表查询例子

大部分参考自http://blog.sina.com.cn/s/blog_7e5541250100ygb1.html，在此基础上，所有的代码我都自己敲了一遍！

1、问题及描述：

学生表

Student(Sid,Sname,Sage,Ssex) --Sid 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

课程表

Course(Cid,Cname,Tid) --Cid --课程编号,Cname 课程名称,T# 教师编号

教师表

Teacher(Tid,Tname) --Tid 教师编号,Tname 教师姓名

成绩表

SC(Sid,Cid,score) --Sid 学生编号,Cid 课程编号,score 分数

2、创建测试数据

create table Student(Sid varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(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');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');create table Teacher(Tid varchar(10),Tname nvarchar(10));insert into Teacher values('01' , '张三');insert into Teacher values('02' , '李四');insert into Teacher values('03' , '王五');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);

3、例子

--1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
--1.1、查询同时存在"01"课程和"02"课程的情况

SELECTa.* , b.score, c.score FROM Student a, sc b, sc cWHERE a.Sid = b.Sid AND a.Sid = c.Sid AND b.Cid = "01" AND c.Cid = "02" AND b.score > c.score

--1.2、查询同时存在"01"课程和"02"课程的情况和存在"01"课程但可能不存在"02"课程的情况(不存在时显示为null)(以下存在相同内容时不再解释)

SELECTa.* , b.score,c.score FROM Student a LEFT JOIN SC b ON a.Sid = b.Sid AND b.Cid = '01'LEFT JOIN SC c ON a.Sid = c.Sid AND c.Cid = '02'where b.score IS NOT NULL

--2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
--2.1、查询同时存在"01"课程和"02"课程的情况

SELECTa.* , b.score, c.score FROM Student a, sc b, sc cWHERE a.Sid = b.Sid AND a.Sid = c.Sid AND b.Cid = "01" AND c.Cid = "02" AND b.score < c.score

--2.2、查询同时存在"01"课程和"02"课程的情况和不存在"01"课程但存在"02"课程的情况

SELECTa.* , b.score,c.score FROM Student a LEFT JOIN SC b ON a.Sid = b.Sid AND b.Cid = '01'LEFT JOIN SC c ON a.Sid = c.Sid AND c.Cid = '02'where c.score IS NOT NULL

--3、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

SELECTa.Sid, a.Sname , AVG(b.score)FROM Student a, sc bWHERE a.Sid = b.SidGROUP BY a.SidHAVING AVG(b.score)>60

--4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩
--4.1、查询在sc表存在成绩的学生信息的SQL语句。

SELECTa.Sid, a.Sname , AVG(b.score)FROM Student a, sc bWHERE a.Sid = b.SidGROUP BY a.SidHAVING AVG(b.score)<60

--4.2、查询在sc表中不存在成绩的学生信息的SQL语句。

SELECTa.Sid, a.Sname , AVG(b.score)FROM Student aLEFT JOIN sc b ON a.Sid = b.SidGROUP BY a.SidHAVING ISNULL(AVG(b.score))

--5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩
--5.1、查询所有有成绩的SQL。

SELECTa.Sid, a.Sname, count(b.Cid) , SUM(b.score)FROM Student aLEFT JOIN sc b ON a.Sid = b.SidGROUP BY a.Sid

--6、查询"李"姓老师的数量
--方法1

SELECTcount(a.Tid)FROM teacher aWHERE a.Tname LIKE "李%"

--方法2

SELECTcount(a.Tid)FROM teacher aWHERE LEFT(a.Tname,1) LIKE "李%"

--7、查询学过"张三"老师授课的同学的信息

SELECTa.*FROM student a, teacher b, sc c, course dWHERE c.Sid = a.Sid AND c.Cid = d.Cid AND d.Tid = b.Tid AND b.Tname = "张三"

--8、查询没学过"张三"老师授课的同学的信息

SELECTa.*FROM student aWHERE a.Sid NOT IN(SELECT DISTINCT b.Sid FROM sc b, course c, teacher dWHERE b.Cid = c.Cid AND c.Tid = d.Tid AND d.Tname = "张三")

--9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
--方法1

SELECTa.*FROM student a, sc b, sc cWHERE a.Sid = b.Sid AND a.Sid = c.Sid AND b.Cid = "01" AND c.Cid = "02"

--方法2

SELECT a.* FROM student a, sc bWHERE a.Sid = b.Sid AND b.Cid = '01' AND EXISTS (SELECT 1 FROM SC c WHERE c.Sid = b.Sid AND c.Cid = '02')

--方法3

SELECT a.* FROM student aWHERE Sid in(SELECT Sid FROM(SELECT DISTINCT Sid FROM sc WHERE Cid = "01"UNION ALLSELECT Sid FROM sc WHERE Cid = "02") t GROUP BY SidHAVING count(1) = 2 )

--10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
--方法1

SELECT a.* FROM student a, sc bWHERE a.Sid = b.Sid AND b.Cid = "01" AND NOT EXISTS(SELECT 1 FROM sc cWHERE a.Sid = c.Sid AND c.Cid = "02" )

--方法2

SELECT a.* FROM student a, sc bWHERE a.Sid = b.Sid AND b.Cid = "01" AND a.Sid NOT IN(SELECT c.Sid FROM sc cWHERE a.Sid = c.Sid and c.Cid ="02")

--11、查询没有学全所有课程的同学的信息
--11.1、没有学习课程则不会列出来

SELECT a.* FROM student a, sc bWHERE a.Sid = b.SidGROUP BY a.SidHAVING count(b.score) < (SELECT count(1) FROM course)

--11.2没学过课程的也会列出来

SELECT a.* FROM student aLEFT JOIN sc b ON a.Sid = b.SidGROUP BY a.SidHAVING count(b.score) < (SELECT count(1) FROM course)

--12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息

SELECT DISTINCT a.* FROM student a, sc b WHERE a.Sid = b.Sid AND b.Cid IN(SELECT DISTINCT c.Cid FROM sc cWHERE c.Sid = "01") AND a.Sid <> "01"

--13、查询和"01"号的同学学习的课程完全相同的其他同学的信息 （开始还想着一个个比较的）

SELECT a.* FROM student a, sc b WHERE a.Sid = b.Sid AND a.Sid <> "01" AND b.Cid IN(SELECT DISTINCT c.Cid FROM sc cWHERE c.Sid = "01") GROUP BY(a.Sid)HAVING count(1) = (SELECT COUNT(1) FROM sc  WHERE sc.Sid = "01")

--14、查询没学过"张三"老师讲授的任一门课程的学生姓名 

--方法1

SELECT a.* FROM student aWHERE a.Sid NOT IN(SELECT DISTINCT a.SidFROM sc b, course c, teacher dWHERE a.Sid = b.Sid AND b.Cid = c.Cid AND c.Tid = d.Tid AND d.Tname = "张三")

--方法2（使用not exists速度更快）

SELECT a.* FROM student aWHERE  NOT EXISTS(SELECT DISTINCT a.SidFROM sc b, course c, teacher dWHERE a.Sid = b.Sid AND b.Cid = c.Cid AND c.Tid = d.Tid AND d.Tname = "张三")

--15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

SELECT a.Sid, a.Sname, AVG(b.score) FROM student a, sc bWHERE a.Sid = b.Sid AND b.score < 60GROUP BY a.SidHAVING count(1) >= 2

--16、检索"01"课程分数小于60，按分数降序排列的学生信息

SELECT a.*FROM student a, sc bWHERE a.Sid = b.Sid AND b.Cid = "01" AND b.score < 60ORDER BY b.score DESC

--17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

SELECT a.Sid ,a.Sname, MAX(CASE c.Cname WHEN "语文" THEN b.score ELSE NULL END) "[语文]",MAX(CASE c.Cname WHEN "数学" THEN b.score ELSE NULL END) "[数学]",MAX(CASE c.Cname WHEN "英语" THEN b.score ELSE NULL END) "[英语]",AVG(b.score) "[平均分]"FROM student aLEFT JOIN sc b on a.Sid = b.SidLEFT JOIN course c on b.Cid = c.CidGROUP BY a.SidORDER BY AVG(b.score) DESC

为什么没有MAX函数的话每行的成绩只有一个有数据？？？