Question

我正在从原件生成图像并将它们存储在表格中。我想要一个检查间隙的查询。

图像尺寸保存在第3张表格中，每张原稿应为类型表格中的每条记录生成1张图像。

到目前为止我所得到的是什么：

SELECT  oi.OriginalImageID, it.ImageTypeID
FROM    dbo.OriginalImages AS oi
CROSS JOIN
        dbo.ImageType AS it
LEFT OUTER JOIN
            (
            SELECT  oi2.OriginalImageID, it2.ImageTypeID
            FROM    dbo.OriginalImages AS oi2
            INNER JOIN
                    dbo.GeneratedImages AS gi2 ON gi2.OriginalImageID = oi2.OriginalImageID
            INNER JOIN
                    dbo.ImageType AS it2 ON it2.ImageTypeID = gi2.ImageTypeID
            ) AS sub ON sub.OriginalImageID = oi.OriginalImageID
                        AND sub.ImageTypeID = it.ImageTypeID
WHERE   (sub.OriginalImageID IS NULL)

哪个有效，但看起来很难看。我想知道是否有一种更优雅的方式来做它。

表格基本上如下：

OriginalImages
    OriginalImageID (PK)
    Image

GeneratedImages
    OriginalImageID (FK)
    ImageTypeID (FK)
    Image

ImageType
    ImageTypeID (PK)
    Description

Answer 1

您应该能够将现有查询简化为：

SELECT  oi.OriginalImageID, it.ImageTypeID
FROM    dbo.OriginalImages AS oi
CROSS JOIN
        dbo.ImageType AS it
LEFT OUTER JOIN
        dbo.GeneratedImages AS gi2 
        ON gi2.OriginalImageID = oi.OriginalImageID AND
        gi2.ImageTypeID = it.ImageTypeID
WHERE   gi2.OriginalImageID IS NULL

虽然我个人会使用NOT EXISTS：

SELECT  oi.OriginalImageID, it.ImageTypeID
FROM    dbo.OriginalImages AS oi
CROSS JOIN
        dbo.ImageType AS it
WHERE NOT EXISTS
        (SELECT NULL FROM dbo.GeneratedImages AS gi2 
         WHERE gi2.OriginalImageID = oi.OriginalImageID  AND
               gi2.ImageTypeID = it.ImageTypeID)

（编辑后评论。）

在桥/数据交叉表中查找“缺失”记录

1 个答案: