在T-Sql中的条件中使用空变量

Question

有没有办法按照以下方式使用变量？

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

还有另一种方法可以做到这一点吗？

谢谢。

Answer 1

你需要做的

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

只为此刻仍然可以完整做

SET ANSI_NULLS OFF 

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

，但你不应该。此选项已弃用。 Quite an interesting related blog post

Answer 2

是否有您要坚持为空的变量，而不是仅仅做一个特殊的原因：

SELECT * 
FROM Market market 
WHERE market.ID IS NULL 

Answer 3

如果你只是想确定是否market.ID为空，你可以这样做

SELECT * 
FROM Market market 
WHERE market.ID IS NULL 

如果您正在测试，看看是否market.ID为空或和其它一些价值试试这个

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