内连接相当于这个子查询？答案

【问题标题】：Inner join equivalent of this subquery?内连接相当于这个子查询？
【发布时间】：2012-09-26 03:02:04
【问题描述】：

我有这些表

BooksCatalog
[BookCatalogID],[BooksCatalogBookID],[ReceivedFrom],[BillNo],[billdate]

Books
[BookID],[BookTitle],[ISBN],[ISBN13],[BookAuthorID],[BookPublisherID],[YearPublished],[NumberOfPages],[Volume],[edition],[Price]

Authors
[AuthorID],[AuthorName],[AuthorCityID],[AuthorStateID],[PhoneNumber],[Email],[Website]

我正在运行这个查询，

SELECT Books.BookTitle FROM Books 
        INNER JOIN Authors ON Authors.AuthorId=Books.BookAuthorID
        WHERE Books.BookID IN 
        (SELECT BooksCatalog.BooksCatalogBookID FROM BooksCatalog
        WHERE BooksCatalog.billdate = (SELECT MIN(BooksCatalog.billdate) FROM BooksCatalog))
        AND
        AUTHORS.AuthorName = @AuthorName;

因为它使用了 2 个子查询，我感觉它没有优化，如果与等效的内部连接一起使用，它可以表现得更好。那么，这个等效的内部连接是什么？我正在做的是找到添加到库中的第一个给定作者。

【问题讨论】：

现代 RDBMS 通常会优化查询，所以我不会担心...

标签： sql-server join subquery

【解决方案1】：

对于在整个架构中使用别名、架构前缀和将元素（例如 BookId 或 AuthorId）命名为相同的东西，有很多话要说。它真的需要被称为 BookAuthorId 或 BooksCatalogBookID 吗？

无论如何，您的查询可以通过这种方式重新编写得更整洁一些，但正如@billy 建议的那样，它可能不会真正受益于完全不同的计划：

SELECT b.BookTitle 
FROM dbo.Books AS b 
INNER JOIN Authors AS a 
ON a.AuthorId = b.BookAuthorID
INNER JOIN 
(
  SELECT BookId = MIN(BooksCatalogBookID)
   FROM dbo.BooksCatalog 
) AS bc
ON bc.BookId = b.BookId
WHERE a.AuthorName = @AuthorName;

您似乎在这里依赖一个非常特殊的连接标准。在目录中的所有书籍中，账单日期最早的书籍也恰好是您确定的一位作者所写的几率是多少？您的逻辑是否真的可能是从指定作者那里获得第一本收费书籍？如果是这样，那么也许这更有意义：

;WITH x(BookTitle, rn) AS
(
  SELECT b.BookTitle, ROW_NUMBER() OVER (ORDER BY bc.billdate)
    FROM dbo.BooksCatalog AS bc
    INNER JOIN b.Books AS b
    ON b.BookId = bc.BooksCatalogBookID
    INNER JOIN dbo.Authors AS a
    ON b.BookAuthorID = a.AuthorID
    WHERE a.AuthorName = @AuthorName
)
SELECT BookTitle FROM x WHERE rn = 1;

【讨论】：

@AaronBertand：是的，这正是我要问的！我需要给定作者的第一本收费书籍。谢谢！

【解决方案2】：

您可以将一个子查询替换为内连接。

            SELECT Books.BookTitle 
              FROM Books 
        INNER JOIN Authors 
                ON Authors.AuthorId = Books.BookAuthorID
        INNER JOIN BooksCatalog 
                ON BooksCatalog.BooksCatalogBookID = Books.BookID 
               AND BooksCatalog.billdate = (SELECT MIN(BooksCatalog.billdate) FROM BooksCatalog) WHERE BooksCatalogBookID = Books.BookID)
        WHERE      Authors.AuthorName = @AuthorName;

【讨论】：