在 BigQuery 中將列轉換為值

Question

我有以下數據：

     date_ country category_A category_B
2022-12-11     USA        100        200
2022-12-11  Canada       2000        400

這是由此查詢生成的：

select
  date('2022-12-11') as date_, 'USA' as country, 100 as category_A, 200 as category_B,
union all select 
  date('2022-12-11') as date_, 'Canada' as country, 2000 as category_A, 400 as category_B

我想做的是只將數據的最后兩列轉換為值，並為值獲取一個列，如下表：

     date_ country   category  value 
2022-12-11     USA category_A    100       
2022-12-11     USA category_B    200        
2022-12-11  Canada category_A   2000   
2022-12-11  Canada category_B    400   

Answer 1

也許它並不完美，但您可以使用以下查詢：

with countries AS
(select
  date('2022-12-11') as date_, 'USA' as country, 100 as category_A, 200 as category_B,
union all select 
  date('2022-12-11') as date_, 'Canada' as country, 2000 as category_A, 400 as category_B
)

select 
  date_,
  country,
  category
from countries,
unnest(array[struct('category_A' AS category_name, category_A AS category_value), struct('category_B' AS category_name, category_B AS category_value)]) as category;

結果是：

在unnest中，您需要添加所有預期的類別列。