CASE WHEN in other columns [closed]

I have a data like this

I tried to use CASE WHEN to sum categories to other columns but my code (bellow) returns NULL-s and work only for one category.

SELECT  
   YEAR(the_date)  
   ,month(the_date)  
  ,CASE WHEN Category IN (N'A','B') THEN SUM(Cost) END Category_1_Cost  
  ,CASE WHEN Category = 'C' THEN SUM(Cost) END Category_2_Cost  
  ,CASE WHEN Category = 'D' THEN SUM(Cost) END Category_3_Cost
 FROM 
  Base
GROUP 
  BY YEAR(the_date), month(the_date) ,  Category

Solution 1:

use this

SELECT  
   YEAR(the_date)  
   ,month(the_date)  
  ,CASE WHEN Category IN ('A','B') THEN SUM(Cost) ELSE 0 END Category_1_Cost  
  ,CASE WHEN Category = 'C' THEN SUM(Cost) ELSE 0 END Category_2_Cost  
  ,CASE WHEN Category = 'D' THEN SUM(Cost) ELSE 0 END Category_3_Cost
 FROM 
  Base
GROUP 
  BY YEAR(the_date), month(the_date) ,  Category

results: