从0.01开始的SQL之路之sql50题

之路之sql50题"/>

从0.01开始的SQL之路之sql50题

 前期准备工作：熟悉几种join，如inner join,left join,right join。

开始学习sql，直接搜索sql50题。点开百度搜索后的第一条链接。

参考链接：

首先是建表语句

-- 学生表Student
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' , '孙⻛' , '1990-12-20' , '男');
insert into Student values('04' , '李云' , '1990-12-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '⼥');
insert into Student values('06' , '吴兰' , '1992-01-01' , '⼥');
insert into Student values('07' , '郑⽵' , '1989-01-01' , '⼥');
insert into Student values('09' , '张三' , '2017-12-20' , '⼥');
insert into Student values('10' , '李四' , '2017-12-25' , '⼥');
insert into Student values('11' , '李四' , '2012-06-06' , '⼥');
insert into Student values('12' , '赵六' , '2013-06-13' , '⼥');
insert into Student values('13' , '孙七' , '2014-06-01' , '⼥');
-- 科目表Course
create table Course(CId varchar(10),Cname nvarchar(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');
-- 教师表Teacher
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');
-- 成绩表SC
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);

好的，下面让我们开始做题

1.查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数

答：这题还是比较简单的，熟悉一下join就能知道怎么写了，需要注意的是a inner join b on和直接a,b where 的用法，但这边还是建议多用用join，代码不一定是越简洁越好，代码规范很重要

select * from student s left join sc c on s.SId=c.SId
where S.SId in (SELECT a.SId from 
(SELECT * from sc where CId=01) a inner join (select * from sc where CId=02) b
on a.SId=b.SId where a.score>b.score)

2.查询同时存在"01"课程和"02"课程的情况

答：这题对比上题来说是显而易见的简单了些许，直接inner join开干

select * from student s inner join 
(select * from sc where CId=01) c
on s.SId=c.SId inner join
(select * from sc where CId=02) d
on s.SId=d.SId

简单。。。输出的列可能多了些，但我是小白嘛，不知道怎么筛选列，就会一个*，嘿嘿

3.查询存在"01"课程但可能不存在"02"课程的情况(不存在时显示为 null ) 

答：跟上题差不多就是把join改成左外就行，easy

select * from student s inner join 
(select * from sc where CId=01) c
on s.SId=c.SId left join
(select * from sc where CId=02) d
on s.SId=d.SId

 4.查询不存在"01"课程但存在"02"课程的情况

答：这题和上题差不多，join