Hive函数之explode和inline

explode和inline函数可以将单列扩展成多列或者多行。
1.explode将单列扩展成多行

select explode(subordinates) from employees;

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explode的参数可以是array还可以是map，如果是map,将生成2个字段，一个是map的键,字段名为key，一个是map的值,字段的名为：value,如下：

select explode(deductions) from employees ;

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explode的限制，如下sql不支持：

• 不能和其他字段一起使用

select name,explode(subordinates) from employees; 

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• 不支持函数嵌套

select explode(explode(subordinates)) from employees 

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• 不能和group by、sort by 和cluster by一起使用

select explode(subordinates) 
from employees 
group by explode(subordinates)

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2.inline
inline的参数形式：inline(ARRAY)
inline一般结合lateral view使用

select t1.col1 as name,t1.col2 as sub1
from employees 
lateral view inline(array(struct(name,subordinates[0]))) t1

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inline 嵌套多个struct,

select t1.col1 as name,t1.col2 as sub
from employees 
lateral view inline(array(struct(name,subordinates[0]),
                          struct(name,subordinates[1]))) t1
where t1.col2 is not null

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还可以给inline的字段取别名：

select t1.name,t1.sub
from employees 
lateral view inline(array(struct(name,subordinates[0]),
                          struct(name,subordinates[1]))) t1 as name,sub
where t1.sub is not null

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