爲什麼SQL允許這種奇怪的IN子句使用？

Question

我正在學習SQL，這裏是一個查詢，我只是跑（從W3學校）：

SELECT * FROM Products 
WHERE (Price BETWEEN 10 AND 20) 
AND NOT (CategoryID in (2 OR 3)) 

類別ID是一個數列，以及正確的使用方法應該是：

AND NOT (CategoryID in (2, 3)) /* give me all rows where categoryID can't be 2 or 3 */ 

所以你怎麼能說：

AND NOT (CategoryID in (2 OR 3)) /* why does SQL allow it? */ 

源 - http://www.w3schools.com/sql/sql_between.asp

Answer 1

如果您在談論SQL Server，請始終轉到源代碼。

http://technet.microsoft.com/en-us/library/bb510741.aspx

對於IN操作符：

http://technet.microsoft.com/en-us/library/ms177682.aspx

下面是從文檔的例子：

USE AdventureWorks2012; 
GO 
SELECT p.FirstName, p.LastName 
FROM Person.Person AS p 
    JOIN Sales.SalesPerson AS sp 
    ON p.BusinessEntityID = sp.BusinessEntityID 
WHERE p.BusinessEntityID IN 
    (SELECT BusinessEntityID 
    FROM Sales.SalesPerson 
    WHERE SalesQuota > 250000); 
GO

這裏，in聲明看着子的結果 - 查詢，一個SELECT語句。

讓我們改變在子查詢的WHERE子句中拉了回來只有兩個BusinessEntityIDs：

USE AdventureWorks2012; 
GO 
SELECT p.FirstName, p.LastName 
FROM Person.Person AS p 
    JOIN Sales.SalesPerson AS sp 
    ON p.BusinessEntityID = sp.BusinessEntityID 
WHERE p.BusinessEntityID IN 
    (SELECT BusinessEntityID 
    FROM Sales.SalesPerson 
    WHERE 
     (BusinessEntityID = 2 OR BusinessEntityID = 3) 
    ); 
GO

基本上是

USE AdventureWorks2012; 
GO 
SELECT p.FirstName, p.LastName 
FROM Person.Person AS p 
    JOIN Sales.SalesPerson AS sp 
    ON p.BusinessEntityID = sp.BusinessEntityID 
WHERE p.BusinessEntityID IN (2,3); 
GO

這是結果子查詢的WHERE (BusinessEntityID = 2 OR BusinessEntityID = 3)，那麼爲什麼不允許語法WHERE p.BusinessEntityID IN (2 OR 3);？