Hive 外部表的练习
hive创建库和表操作
hive加载数据，4种发放
1.数据放在Linux创建表结构 进行加载
2.先定义表结构、将一个查询select语句结果插入到表中
3.数据先放在hdfs 创建表结构 进行加载(hive 只能加载目标文件的上级目录)
4.外部数据 external 内部表和外部表 使用上没有任何区别，删除时则有差别数据：
创建表，以及添加数据：
create external table if not exists my_course(
courseid string,
couresename string
)
row format delimited fields terminated by ','
stored as textfile
location '/hive/my_course';
create external table if not exists my_source(
userid string
courseid string,
score string
)
row format delimited fields terminated by ','
stored as textfile
location '/hive/my_sourcet'
create external table if not exists my_student(
userid string
name string
sex string
age string,
xi string
)
row format delimited fields terminated by ','
stored as textfile
location '/hive/my_student'
1.问题：查询全体学生的学号与姓名
select
userid,name
from my_student;
2.问题：查询选修了课程的学生姓名和课程名称
select student.name,t.couresename
from(
select course.couresename couresename,score.userid userid
from my_score score,my_course course
where score.courseid=course.courseid) t,my_student student
where t.userid=student.userid;
3.问题：查询每个选修的课程共选了多少人
select t.couresename,count(*) num
from(
select course.couresename couresename,score.userid userid
from my_score score,my_course course
where score.courseid=course.courseid) t,my_student student
where t.userid=student.userid
group by t.couresename
order by num desc
limit 3;
4.问题：查询学生的总人数
select count(distinct(userid))
from my_student;
5.问题：计算数据库课程的学生平均成绩
select course.couresename,avg(score.score)
from my_score score,my_course course
where course.couresename='数据库' and score.courseid=course.courseid
group by course.couresename;
6.问题：查询选修数学课程的学生最高分数
select max(score.score)
from my_score score,my_course course
where course.couresename='数学' and score.courseid=course.courseid;
7.问题：查询选修了3门以上的课程的学生姓名
select student.name,t.num
from(
select userid,count(*) num
from my_score
group by userid ) t,my_student student
where t.userid =student.userid and t.num>=3;
8.问题：按照年龄排序并直接输出到不同的文件中
create table if not exists result2(
userid string,
name string,
sex string,
age string,
xi string
)
row format delimited fields terminated by ','
stored as textfile;
insert into result2
select *
from my_student
order by age desc;
9.问题：查询学生的得分情况。
select student.name,score.score
from my_score score,my_student student
where score.userid=student.userid;
10.问题：查询选修信息系统课程且成绩在90分以上的所有学生。
select distinct(t2.name)
from(
select score.userid userid
from my_score score,my_course course
where score.score>=90 and score.courseid=course.courseid) t1,my_student t2
where t1.userid=t2.userid;
11.问题：查询与“刘晨”在同一个系学习的其他学生
select t3.name
from(
select t2.name name
from my_student t1,my_student t2
where t1.name='刘晨' and t1.xi=t2.xi) t3
where t3.name<>'刘晨';
