MYSQL50道基础练习题

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);

学生

老师

课程

分数

01

查询"01"课程比"02"课程成绩高的学生的信息及课程分数

先查询01课程

再查询02

交集

SELECT 
	* 
FROM 
  (SELECT * FROM SC WHERE cid='01') a
	JOIN
	(SELECT * FROM SC WHERE cid='02') b on a.sid = b.sid

增加限制条件，01分数 > 02分数

关联查询课程信息

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

关联查询学生信息

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

汇总

-- 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

先查询平均分

SELECT 
	*,
	AVG(score) avg
FROM sc
GROUP BY sc.sid
HAVING avg >= 60

再多表关联查询

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