Hive案例05-学生成绩表综合案例

1. 数据说明

(1) student表

hive> select * from student;

# 学生ID    学生姓名     性别    年龄    所在系
# sid       sname       sex     age     dept
  95002     Aiden       female  19      IS
  95017     Jacob       female  18      IS
  95018     Ethan       female  19      IS
  95013     Matthew     male    21      CS
  95014     Nicholas    female  19      CS
......

(2) course表

hive> select * from course;

# 课程ID    课程名称
# cid       cname
  1         Chinese
  2         Math
  3         English
  4         Physics
  5         Chemistry
  6         Biology

(3) sc表

hive> select * from sc;

# 学生ID    课程ID  成绩
# sid       cid     score
  95001     1       81
  95001     2       85
  95001     3       88
  95001     4       70
  95002     2       90
......

2. SQL查询练习题目

(1) 基本练习

<1> 查询全体学生的学号与姓名

select sid, sname from student;

<2> 查询选修了课程的学生姓名

select distinct sid from sc;

(2) hive的group by和集合函数

<1> 查询学生的总人数

select count(*) from student;

<2> 计算1号课程的学生平均成绩

select cid, avg(score) from sc
where cid = '1'
group by cid;

<3> 查询各科成绩平均分

select c.cname, tmp.avg_score from
course c join
(select cid, avg(score) avg_score from sc
group by cid) tmp
on c.cid = tmp.cid;

/*
Chinese     83.66666666666667
Math        88.66666666666667
English     81.46153846153847
Physics     83.125
Chemistry   85.0
Biology     89.45454545454545
*/

<4> 查询1号课程的最高分数

select cid, max(score) max_score from sc
where cid = '1'
group by cid;

/*
1   98
*/

<5> 求各个课程号及相应的选课人数

select cid, count(distinct sid) count_sid from sc
group by cid;

/*
1   15
2   15
3   13
4   16
5   12
6   11
*/

<6> 查询选修了3门以上的课程的学生学号

select sid, count(distinct cid) count_cid from sc
group by sid
having count_cid > 3;

/*
95001   4
95002   4
95004   4
95005   4
95006   6
95007   4
95011   4
95012   4
95013   4
95015   4
95018   4
95019   5
95022   4
*/

(3) hive的order by/sort by/distribute by

<1> 查询学生信息，结果按学号全局有序

select * from student
order by sid;

<2> 查询学生信息，结果区分性别按年龄有序

set mapred.reduce.tasks=2;(默认-1)

select * from student
distribute by sex
sort by age;

/*
95009   Alexande    female  18  MA
95017   Jacob       female  18  IS
95008   Zachary     female  18  CS
95014   Nicholas    female  19  CS
95019   Jack        female  19  IS
95018   Ethan       female  19  IS
95002   Aiden       female  19  IS
95007   Jaden       female  19  MA
95012   Andrew      female  20  CS
95003   Michael     female  22  MA
95021   Connor      male    17  MA
95005   Tyler       male    18  MA
95011   Noah        male    18  MA
95015   Jackson     male    18  MA
95010   Caden       male    19  CS
95004   Ryan        male    19  IS
95022   Logan       male    20  MA
95001   Caleb       male    20  CS
95020   Joshua      male    21  IS
95013   Matthew     male    21  CS
95016   Brayden     male    21  MA
95006   Dylan       male    23  CS
*/

(4) join查询

<1> 查询每个学生及其选修课程的情况

select s.sname, c.cname from
student s join sc on s.sid = sc.sid
join course c on c.cid = sc.cid;

/*
Caleb   Chinese
Caleb   Math
Caleb   English
Caleb   Physics
Aiden   Math
Aiden   English
Aiden   Physics
Aiden   Chemistry
Michael Chinese
Michael English
......
*/

<2> 查询学生的得分情况

select s.sname, c.cname, sc.score from
student s join sc on s.sid = sc.sid
join course c on c.cid = sc.cid;

/*
Noah    Chinese 81
Noah    Math    91
Noah    English 81
Noah    Physics 86
Andrew  Chinese 81
Andrew  English 78
Andrew  Physics 85
Andrew  Biology 98
......
*/

<3> 查询选修2号课程且成绩在90分以上的所有学生

select s.sname, sc.cid, sc.score from
student s join sc on s.sid = sc.sid
where sc.cid = '2' and sc.score > 90;

/*
Ryan        2   92
Tyler       2   92
Caden       2   98
Noah        2   91
Nicholas    2   100
Brayden     2   99
Ethan       2   100
Joshua      2   99
Connor      2   93
*/

<4> 查询所有学生的信息，如果在成绩表中有成绩，则输出成绩表中的课程号

select s.*, sc.cid from
student s left join sc
on s.sid = sc.sid;

/*
......
95015   Jackson male    18  MA  1
95015   Jackson male    18  MA  3
95015   Jackson male    18  MA  4
95015   Jackson male    18  MA  6
95016   Brayden male    21  MA  1
95016   Brayden male    21  MA  2
95016   Brayden male    21  MA  4
*/

(5) LEFT SEMI JOIN

查询与"Jackson"在同一个系学习的学生

select student.sname, student.dept from student left semi join
(select dept from student where sname = 'Jackson') tmp
on student.dept = tmp.dept;

/*
Michael     MA
Tyler       MA
Jaden       MA
Connor      MA
Logan       MA
Noah        MA
Alexande    MA
Jackson     MA
Brayden     MA
*/