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
*/
