在T-Sql中的條件中使用空變量

Question

有沒有辦法按照以下方式使用變量？

DECLARE @ID int; 
SET @ID = NULL; 
SELECT * 
FROM Market market 
WHERE market.ID IS @ID 

還有另一種方法可以做到這一點嗎？

謝謝。

Answer 1

你需要做的

SELECT * 
FROM Market market 
WHERE market.ID = @ID OR (@ID IS NULL AND market.ID IS NULL) 

只爲此刻仍然可以完整做

SET ANSI_NULLS OFF 

SELECT * 
FROM Market market 
WHERE market.ID = @ID 

，但你不應該。此選項已棄用。 Quite an interesting related blog post

Answer 2

是否有您要堅持爲空的變量，而不是僅僅做一個特殊的原因：

SELECT * 
FROM Market market 
WHERE market.ID IS NULL 

Answer 3

如果你只是想確定是否market.ID爲空，你可以這樣做

SELECT * 
FROM Market market 
WHERE market.ID IS NULL 

如果您正在測試，看看是否market.ID爲空或和其它一些價值試試這個

SELECT * 
FROM Market market 
WHERE market.ID IS NULL 
    OR market.ID = @ID