SQL选择列以更新CASE条件

Question

我有ArticlePhotos表，每篇文章都可以有N张照片。我正在编写一个触发器，它将反映在ArticlePhotos表中所做的更改，以在Article表中创建一个平面的hierarhy，以便在列出多篇文章时更快地查询以避免连接。

有没有办法在某种CASE子句中选择要更新的列，而是为每种所需类型编写update子句

DECLARE @FrontPagePhotoTypeId INT = 1; 
DECLARE @MainArticlePhotoTypeId INT = 2; 
DECLARE @FacebookPhotoType INT = 4; 


-- all deleted photo records should be set as null in Articles table (flat hierarchy)

-- delete frontpage photo
UPDATE Articles 
SET Articles.FrontPagePhoto = NULL <-- can this be written as a case by PhotoTypeId
FROM Articles 
INNER JOIN deleted 
ON Articles.id = deleted.ArticleId WHERE deleted.PhotoTypeId = @FrontPagePhotoTypeId 

-- delete Main Article Photo
UPDATE Articles 
SET Articles.MainArticlePhoto = NULL
FROM Articles 
INNER JOIN deleted 
ON Articles.id = deleted.ArticleId WHERE deleted.PhotoTypeId = @MainArticlePhotoTypeId 

-- delete facebook
UPDATE Articles 
SET Articles.FacebookPhoto = NULL
FROM Articles 
INNER JOIN deleted 
ON Articles.id = deleted.ArticleId WHERE deleted.PhotoTypeId = @FacebookPhotoType 

Answer 1

上述查询可以重写为单个更新，如下所示

DECLARE @FrontPagePhotoTypeId INT = 1; 
DECLARE @MainArticlePhotoTypeId INT = 2; 
DECLARE @FacebookPhotoType INT = 4; 

UPDATE Articles 
SET 
    FrontPagePhoto = case when deleted.PhotoTypeId = @FrontPagePhotoTypeId
                                        then null
                                    else Articles.FrontPagePhoto end,
    MainArticlePhoto = case when deleted.PhotoTypeId = @MainArticlePhotoTypeId 
                                        then null
                                    else Articles.MainArticlePhoto end,
    FacebookPhoto = case when deleted.PhotoTypeId = @FacebookPhotoType 
                                        then null
                                    else Articles.FacebookPhoto end                             
FROM Articles 
INNER JOIN deleted 
ON Articles.id = deleted.ArticleId