您可以使用（假）聚合函数，例如：max（）（最好使用null而不是0）

SELECT max(CASE
        WHEN DI.item_type = 'in_list' 
          AND DI.item_method = 'item_category' 
          AND DC.condition_method ='condition_time'  
        THEN 'TimeDiscount' 
      ELSE null END )AS TimeDiscount,
       max(CASE 
          WHEN DI.item_type = 'in_list'  
            AND DI.item_method = 'item_category' 
            AND DC.condition_method ='condition_date'  
          THEN 'DateDiscount' 
          ELSE null END) AS DateDiscount
  FROM srampos_discount_item_list DIL 
  JOIN srampos_discount_items DI ON DI.id = DIL.discount_item_id 
  JOIN srampos_discounts D ON D.id = DI.discount_id 
  JOIN srampos_discount_conditions DC ON D.id = DC.discount_id 
  WHERE DIL.item_id =1