Hive行轉列和列轉行

優點：好理解

缺點：多次select同一張表，造成計算量成倍增加；**冗餘，單個select條件複雜後會變得較難維護。

-- concat('height',':',height,',','weight',':',weight,',','age',':',age) as value

select id, 'height' as label, height as value
from tmp1 
union all 
select id, 'weight' as label, weight as value
from tmp1 
union all 
select id, 'age' as label, age as value
from tmp1

缺點：如果value是數值型，concat後數值型將轉換為string型，展開後要多一層轉換。

-- 最後將info的內容切分

-- 注意：value列按需轉換為int/bigint型
select id
,split(info,':')[0] as label
,split(info,':')[1] as value
from 
( -- 先將資料拼接成「height:180,weight:60,age:26」
select id
,concat('height',':',height,',','weight',':',weight,',','age',':',age) as value
from tmp1 
) as tmp1
lateral view explode(split(value,',')) mytable as info; -- 然後在借用explode函式將資料膨脹至多行

優點：沒發現

select  a.id    as id 

,tmp1.value as height 
,tmp2.value as weight 
,t***.value as age
from (
select id from tmp2
group by id 
) a 
left join (
select id 
,label 
,value
from tmp2
where label = 'height' 
) as tmp1join on a.id = tmp1.id
left join (
select id 
,label 
,value
from tmp2
where label = 'weight' 
) as tmp2join on a.id = tmp2.id
join 
( select id 
,label 
,value
from tmp2
where label = 'age' 
) as t*** on a.id = t***.id;

缺點：計算過程增加了多餘的sum()/max()步驟

select id

, sum(if(label='height', value, 0)) as height
, sum(if(label='weight', value, 0)) as weight
, sum(if(label='age', value, 0)) as age
from tmp2
group by id

缺點：concat+ collect_set + concat_ws + str_to_map 比較難理解。

select  id

,tmpmap['height'] as height
,tmpmap['weight'] as weight
,tmpmap['age'] as age
from 
( select id
,str_to_map(concat_ws(',',collect_set(concat(label,':',value))),',',':') as tmpmap
from tmp2
group by id 
) as tmp1;

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