问题描述
CREATE TABLE BlogPosts ( PostID INT PRIMARY KEY not null, PostTitle NVARCHAR , BlogID int, TotalComments int )
可以使用任何 Join 而不是相关子查询来简化此查询吗?
May this query be simplified with any Join instead of correlated subquery?
SELECT TOP 5 * FROM BlogPosts as t0 WHERE t0.PostID = (SELECT TOP 1 t1.PostID FROM BlogPosts as t1 WHERE t0.BlogID = t1.BlogID ORDER BY t1.TotalComments DESC)
我需要来自不同博客的 5 篇文章的总评论数上限.
I need 5 posts with max TotalComments from different blogs.
更新.SQL Server,但我更喜欢标准 SQL
UPD. SQL Server, but I would prefer standard SQL
推荐答案
如果我理解正确,postid 是唯一的,所以这应该会有所帮助
If i understand correctly, postid is unique, so this should help
好的试试这个然后
DECLARE @BlogPosts TABLE ( PostID INT PRIMARY KEY not null, PostTitle NVARCHAR , BlogID int, TotalComments int ) INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 1, 'A', 1, 3 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 2, 'B', 1, 4 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 3, 'C', 2, 5 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 4, 'D', 2, 6 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 5, 'E', 2, 7 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 6, 'F', 1, 8 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 7, 'G', 3, 9 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 8, 'H', 4, 10 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 9, 'I', 5, 11 INSERT INTO @BlogPosts (PostID,PostTitle,BlogID,TotalComments) SELECT 10, 'J', 6, 5 SELECT TOP 5 * FROM @BlogPosts bp INNER JOIN ( SELECT BlogID, MAX(TotalComments) MaxComments FROM @BlogPosts GROUP BY BlogID ) maxCommentsPerBlog ON bp.BlogID = maxCommentsPerBlog.BlogID AND bp.TotalComments = maxCommentsPerBlog.MaxComments ORDER BY bp.TotalComments DESC
不过,您可能有多个最大 blog-totalComments 组合.
You might have multiple max blog-totalComments combinations though.