sql - SQL IN clause which is guaranteed to evaluate to false

Question

Is there any value which I can place in a SQL IN clause which will guarantee that the clause will evaluate to false?

SELECT *
FROM Products
WHERE ProductID IN (???)

Is there anything I could replace ??? with to guarantee no rows will be returned?

Answer 1

替换为NULL。没有更好的保证！

因为没有其他值可以等于NULL，甚至NULL它本身。

这对于任何类型来说都是一种普遍的价值（正如@zohar-peled 提到的）。

Answer 2

利用NULL

SELECT *
FROM Products
WHERE ProductID IN (NULL)

因为这不会返回任何内容

Answer 3

放入一些最初无效的 ProductID，例如-1.

SELECT *
FROM Products
WHERE ProductID IN (-1)

Answer 4

尝试

SELECT *
FROM Products
WHERE ProductID IN (0)

我很确定您没有 ID=0 的产品

那将返回错误。

Answer 5

SELECT *
FROM Products
WHERE ProductID IN (SELECT '')

另一种可能的方式。