在T-Sql中的条件中使用Null变量

Question

有没有办法以下列方式使用变量？

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

或者还有另一种方法吗？

感谢。

Answer 1

你需要做

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

目前仍然可以完成

SET ANSI_NULLS OFF

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

但你不应该。不推荐使用此选项。 Quite an interesting related blog post

Answer 2

是否有一个特殊原因是您试图将null粘贴到变量中而不是仅仅执行：

SELECT *
FROM Market market
WHERE market.ID IS NULL

Answer 3

如果您只是想确定market.ID是否为null，那么您可以这样做

SELECT *
FROM Market market
WHERE market.ID IS NULL

如果您正在测试以查看market.ID是否为null或其他值，请尝试此

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