Question

我正在学习SQL，这是我刚刚运行的一个查询（来自W3学校）：

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

CategoryID是一个数字列，正确的用法应该是：

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

那么你怎么能说：

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

消息来源 - http://www.w3schools.com/sql/sql_between.asp

Answer 1

如果您正在谈论SQL Server，请始终转到源代码。

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

对于IN运算符：

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

以下是文档中的示例：

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

这里，IN语句正在查看子查询的结果，即SELECT语句。

让我们更改子查询中的WHERE子句，只返回两个BusinessEntityID：

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

这是子查询的WHERE ( BusinessEntityID = 2 OR BusinessEntityID = 3 )的结果，为什么不允许语法WHERE p.BusinessEntityID IN (2 OR 3);？

为什么SQL允许这种奇怪的IN子句使用？

1 个答案: