Hive lateral view 和 explode 详解

1. 建表语句结构 

create table if not exists employees ( 
name         string, 
salary       float, 
subordinates array<string>, 
deductions   map<string, float>, 
address      struct<street:string, city:string, state:string, zip:int> 
) 
row format delimited 
fields terminated by '\001'  
collection items terminated by '\002'  
map keys terminated by '\003' 
lines terminated by '\n' 
stored as textfile;

2. 表里 name 和 subordinates 的数据结构

3. 使用 lateral view 和 explode 查询

select name,subordinate from employees lateral view explode(subordinates) subordinates_table as subordinate;

总结: explode就是将hive一行中复杂的 array 或者 map 结构拆分红多行。

下面就作个小例子, 建立 hive 表 doc, 表里只有一列 text 类型为 string, 将 hadoop 目录下的 README.txt 导入该表, 并写出 sql 求出 wordcount

create table if not exists doc(text string) row format delimited lines terminated by '\n';

load data local inpath '/opt/hadoop-2.7.4/README.txt' overwrite into table doc;

select word, count(*) from doc lateral view explode(split(text,' ')) ITable as word group by word;