hive 常用的 join 操作 实例

test_a 表

id	value
1	java
2	python
3	c++

test_b 表

id	value
1	java
2	go
3	php
4	c++

1. join

计算的是笛卡尔积，不推荐使用

select * from test_a join test_b on test_a.value = test_b.value;

查询结果：
java  java
c++   c++

2. left outer join & right outer join

注意：最好将小表放在 左 | 右

select * from test_a left outer join test_b on test_a.value = test_b.value; 

查询结果：
java    java
python  NULL
c++     c++ 

select * from test_a right outer join test_b on test_a.value = test_b.value; 

查询结果：
java    java
NULL    go
NULL    php
c++     c++

3. full join

select * from test_a full outer join test_b on test_a.value = test_b.value; 

查询结果：
java    java
python  NULL
NULL    go
NULL    php
c++     c++

4. left semi join

select * from test_a left semi join test_b on test_a.value = test_b.value;
等价于：
select * from test_a left outer join test_b on test_a.value = test_b.value where test_b.value is not null; 

查询结果：
java  java
c++   c++