sql查询50题

一个项目涉及到的50个Sql语句
问题及描述：
--1.学生表
Student(S#,Sname,Sage,Ssex) --S# 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
--2.课程表 
Course(C#,Cname,T#) --C# --课程编号,Cname 课程名称,T# 教师编号
--3.教师表 
Teacher(T#,Tname) --T# 教师编号,Tname 教师姓名
--4.成绩表 
SC(S#,C#,score) --S# 学生编号,C# 课程编号,score 分数

---

 

--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');
insert into Student values('09' , '孙吴昊' , '1990-01-20' , '女');
insert into Student values('10' , '赵雷' , '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');
insert into Course values('04' , '英语' , '01');

create table Teacher(
Tid varchar(10),
Tname varchar(10)
);

insert into Teacher values('01' , N'张三');
insert into Teacher values('02' , N'李四');
insert into Teacher values('03' , N'王五');
insert into Teacher values('04' , N'汪二蛋');

 

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);
insert into SC values('08' , '03' , 98);
insert into SC values('09' , '03' , 98);
insert into SC values('10' , '04' , 59);

1、查询平均成绩大于60分的同学的学号和平均成绩；

分组一般结合聚合函数应用

SELECT Sid, AVG(score) AS num_score FROM sc GROUP BY Sid HAVING AVG(score) > 60;
//先得到每个学号和平均分数（应用聚合函数和分组，7个学生），然后在刷选出平均数>60的学生（对分组刷选用having）

// group by后面不能接where，having代替了where

2、查询所有同学的学号、姓名、选课数、总成绩