使用WHEN或IF語句的SQL語句

Question

我現在正在努力學習一下SQL查詢。我想知道有人可以幫忙嗎？

我想傳遞一個字符串存儲過程中的一個，並根據我想在WHERE子句

稍微修改查詢帕拉姆字符串可以爲任意字母或類別ID

ALTER procedure [dbo].[procProductShow] 
    @Alphabet varchar(3) = 'ALL' 
AS 
    IF @Alphabet = 'ALL' or @Alphabet = 'A' OR @Alphabet = 'B' OR @Alphabet = 'C' --- UNTIL Z 
     SELECT 
      Product.ProdID, 
      Product.ProdImgThumbnailLoc, 
      Product.ProdImgThumbnailAltText 

     FROM 
      ProductCategory 
      INNER JOIN Product ON ProductCategory.ProdID = Product.ProdID 
      INNER JOIN Category ON ProductCategory.CatID = Category.CatID 

     WHERE 
      Product.ProdShowOnWeb = 1 AND 
      Category.ShowOnReport = 1 AND    
      (@Alphabet = 'ALL' OR Product.ProdHeading LIKE @Alphabet + '%')  
     ORDER BY Product.ProdHeading 

    ELSE 
     SELECT 
      Product.ProdID, 
      Product.ProdImgThumbnailLoc, 
      Product.ProdImgThumbnailAltText 

     FROM 
      ProductCategory 
      INNER JOIN Product ON ProductCategory.ProdID = Product.ProdID 
      INNER JOIN Category ON ProductCategory.CatID = Category.CatID    
     WHERE 
      Product.ProdShowOnWeb = 1 AND 
      Category.ShowOnReport = 1 AND    
      Category.CatId = @Alphabet   
     ORDER BY Product.ProdHeading 

Answer 1

實際上，你可以簡化這個查詢，這樣你就不需要做長IF語句：

ALTER procedure [dbo].[procProductShow] 
    @Alphabet varchar(3) = 'ALL' 
AS 
    SELECT 
     Product.ProdID, 
     Product.ProdImgThumbnailLoc, 
     Product.ProdImgThumbnailAltText 
    FROM 
     ProductCategory 
     INNER JOIN Product ON ProductCategory.ProdID = Product.ProdID 
     INNER JOIN Category ON ProductCategory.CatID = Category.CatID 
    WHERE 
     Product.ProdShowOnWeb = 1 AND 
     Category.ShowOnReport = 1 AND    
     (@Alphabet = 'ALL' 
      OR (@Alphabet LIKE '[A-Z]' AND Product.ProdHeading LIKE @Alphabet + '%') 
      OR Category.CatId = @Alphabet) 
    ORDER BY Product.ProdHeading 

的@Alphabet LIKE '[A-Z]'噸的一部分他在哪裏條件將執行一個正則表達式來檢查@Alphabet是否只包含通過'Z'的'A'