如何從選擇「as」獲取值

Question

我有以下內容，並且我試圖從AS部分中的「id_category」中獲取值。我需要把它引用到內置的鏈接越往下查詢

case 
    when pa.category_id = 310 then 669 -- Trains 
    when pa.category_id = 309 then 2785 -- Ships 
    when pa.category_id = 311 then 631 -- Planes 
    end 
     else concat("NOT FOUND FOR ",pc.name) 
    end **as "id_category",** 

Answer 1

您將獲得它在外部查詢像

select id_category, ... 
from (
select case 
    when pa.category_id = 310 then 669 -- Trains 
    when pa.category_id = 309 then 2785 -- Ships 
    when pa.category_id = 311 then 631 -- Planes 
     else concat("NOT FOUND FOR ",pc.name) 
    end as "id_category" from table1) xxx; 

Answer 2

你只能我們在爲了通過的id_category聲明。如果您想在其他地方使用它，請嘗試使用子查詢

Select SUBQUERY.id_category 
from (select 

case 
    when pa.category_id = 310 then 669 -- Trains 
    when pa.category_id = 309 then 2785 -- Ships 
    when pa.category_id = 311 then 631 -- Planes 
    end 
     else concat("NOT FOUND FOR ",pc.name) 
    end **as "id_category",** 
... 
) AS 'SUBQUERY' 
...