Hive学习笔记——保存select结果，Join，多重插入

1. 保存select查询结果的几种方式：

1、将查询结果保存到一张新的hive表中

create table t_tmp
as
select * from t_p;

2、将查询结果保存到一张已经存在的hive表中(用load的时候，可以是into或者overwrite into，这里是into或者overwrite)

insert into/overwrite table t_tmp
select * from t_p;

3、将查询结果保存到指定的文件目录（可以是本地，也可以是hdfs）

insert overwrite local directory '/home/hadoop/test'
select * from t_p;

insert overwrite directory '/aaa/test'
select * from t_p;

2. 关于hive中的各种join

准备数据
1,a
2,b
3,c
4,d
7,y
8,u

2,bb
3,cc
7,yy
9,pp

建表：

create table a(id int,name string)
row format delimited fields terminated by ',';

create table b(id int,name string)
row format delimited fields terminated by ',';

导入数据：

load data local inpath '/home/hadoop/a.txt' into table a;
load data local inpath '/home/hadoop/b.txt' into table b;

实验：
** inner join

select * from a join b on a.id=b.id;

+-------+---------+-------+---------+--+
| a.id | a.name | b.id | b.name |
+-------+---------+-------+---------+--+
| 2 | b | 2 | bb |
| 3 | c | 3 | cc |
| 7 | y | 7 | yy |
+-------+---------+-------+---------+--+

**left join

select * from a left outer join b on a.id=b.id;

+-------+---------+-------+---------+--+
| a.id | a.name | b.id | b.name |
+-------+---------+-------+---------+--+
| 1 | a | NULL | NULL |
| 2 | b | 2 | bb |
| 3 | c | 3 | cc |
| 4 | d | NULL | NULL |
| 7 | y | 7 | yy |
| 8 | u | NULL | NULL |
+-------+---------+-------+---------+--+

**right join

select * from a right outer join b on a.id=b.id;

同上效果，只不过这次b的全部显示，a的会有NULL。

**full join

select * from a full outer join b on a.id=b.id;

+-------+---------+-------+---------+--+
| a.id | a.name | b.id | b.name |
+-------+---------+-------+---------+--+
| 1 | a | NULL | NULL |
| 2 | b | 2 | bb |
| 3 | c | 3 | cc |
| 4 | d | NULL | NULL |
| 7 | y | 7 | yy |
| 8 | u | NULL | NULL |
| NULL | NULL | 9 | pp |
+-------+---------+-------+---------+--+

**left semi join

select * from a left semi join b on a.id = b.id;

+-------+---------+--+
| a.id | a.name |
+-------+---------+--+
| 2 | b |
| 3 | c |
| 7 | y |
+-------+---------+--+

3. 多重插入

from student
insert into table student_p partition(part='a')
select * where id<95011;
insert into table student_p partition(part='a')
select * where id<95011;