CASE語句在WHERE子句不工作我錯過了什麼？

Question

試圖在WHERE子句中使用CASE語句，它給我提供了錯誤。我錯過了什麼？

SELECT DISTINCT 
     Commodity, 
     Commodity_ID, 
     [Description], 
     Train, 
     Truck 
FROM dbo.List_Commodity 
WHERE 
     CASE WHEN @Truck = 1 THEN 
      Truck = @Truck 
     WHEN @Train = 1 THEN 
      Train = @Train 
     END 

Answer 1

代替CASE聲明使用AND/OR邏輯做你想要檢索的所有記錄這個

SELECT DISTINCT commodity, 
       commodity_id, 
       [description], 
       train, 
       truck 
FROM dbo.list_commodity 
WHERE (@Truck = 1 
     AND truck = @Truck) 
     OR (@Train = 1 
      AND train = @Train)  

如果當兩個@Truck和@Train不等於1然後添加以下條件以上查詢

 OR (@Train <> 1 
      AND @Train <> 1)  

Answer 2

如果您期待THEN truck = @Truck w生病返回true或false那麼你錯過了MS SQL沒有布爾數據類型和布爾表達式的事實。

Answer 3

如果你仍然想使用CASE語句，下面的查詢會有所幫助：

DECLARE @Truck INT = 1 -- 1 is an example 
DECLARE @Train INT = 1 -- 1 is an example 

SELECT DISTINCT 
     Commodity, 
     Commodity_ID, 
     [Description], 
     Train, 
     Truck 
FROM dbo.List_Commodity 
WHERE 1 = 
     (
      CASE 
       WHEN @Truck = 1 AND Truck = @Truck THEN 1 
       WHEN @Train = 1 AND Train = @Train THEN 1 
      END 
     ) 

P.S：請注意，CASE語句只返回應在此相比，它的值。