【校招VIP】数据库基础之sql五十道题

考点介绍：

数据库在测试工程师的面试过程中也是常问的一项。面试有一定的层次性，如bat级别公司每个点都会深入，而有些公司则只会问到表层，所以每个领域都分为必须掌握和深入了解这两个部分。

本期分享的数据库基础之sql五十道题，分为试题、文章以及视频三部分。

答案详情解析和文章内容可扫下方二维码或链接即可查看！

一、考点题目

测试用数据表

1. 学生表 Student

--SId 学生编号, Sname 学生姓名, Sage 出生年月, Ssex 学生性别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' , '1990-12-20' , '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');

2. 课程表 Cours

--CId 课程编号, Cname 课程名称, TId 教师编号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')

3. 教师表 Teache

--TId 教师编号, Tname 教师姓名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')

4. 成绩表 SC

--SId 学生编号, CId 课程编号, score 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)

1.查询各科成绩最高分、最低分和平均分：以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率（及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90

正确答案：

select Cid, Course.Cname,sum(case when score >= 90 then 1 else 0 end) * 100 / count(score) as '优秀率',sum(case when score >= 80 and score < 90 then 1 else 0 end) * 100 / count(score) as '优良率',sum(case when score >= 70 and score < 80 then 1 else 0 end) * 100 / count(score) as '中等率',sum(case when score >= 60 then 1 else 0 end) * 100 / count(score) as '及格率',max(score) as '最高分',min(score) as '最低分',avg(score) as '平均分'from SC group by Cid;

2. 成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

正确答案：

select Student.*, SC.score from Student, SC, Course, Teacherwhere Student.Sid = SC.Sid and SC.Cid = Course.Cid and Course.Tid = Teacher.Tid and Teacher.Tname = '张三'order by SC.score desclimit 1;

3.查询各科成绩前三名的记录

正确答案：

select a.Cid, a.Sid, a.score, count(b.score) + 1 from(select * from SC group by Cid, Sid, score) aleft join (select * from SC group by Cid, Sid, score) bon a.Cid = b.Cid and a.score < b.scoregroup by a.Cid, a.Sid, a.score having count(b.score) < 3order by a.Cid asc, a.score desc;

4.统计各科成绩各分数段人数：课程编号，课程名称，[100-85]，[85-70]，[70-60]，[60-0] 及所占百分比

正确答案：

select SC.Cid, Course.Cname, count(SC.Sid)sum(case when score >= 85 then 1 else 0 end) * 100 / count(score) as '[100-85]',sum(case when score >= 70 and score < 85 then 1 else 0 end) * 100 / count(score) as '[85-70]',sum(case when score >= 60 and score < 70 then 1 else 0 end) * 100 / count(score) as '[70-60]',sum(case when score >= 0 and score < 60 then 1 else 0 end) * 100 / count(score) as '[60-0]'from SC, Coursewhere SC.Cid = Course.Cidgroup by Cid;

5.按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺

正确答案：

select a.cid, a.sid, a.score, count(b.score)+1 as rankfrom SC as aleft join SC as bon a.score<b.score and a.cid = b.cidgroup by a.cid, a.sid, a.scoreorder by a.cid, rank ASC;

（答案点击下方链接或者扫海报二维码查看哦）

二、考点文章

sql经典50题

观察原始表格数据，在excel中想得到01比02高，我们需要将原始表格拆分成两个表，课程01表和课程02表，再进行vlookup得到c表，根据if条件判断筛出最终数据。

重点是：1.拆表 2.匹配,转成SQL语言

（扫下方海报二维码查看完整版）

三、考点视频

二叉树叶子结点数=度为2结点数+1

这是二叉树最常考的性质之一，是校招和考研笔试的考点。性质有数学的定理一样，掌握了这种题就是送分题，没掌握花很长时间也得不了分

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