상관 하위 쿼리 대신 조인

Question

CREATE TABLE BlogPosts 
(
PostID INT PRIMARY KEY not null, 
PostTitle NVARCHAR , 
BlogID int, 
TotalComments int 
) 

이 쿼리를 상관 하위 쿼리 대신 단순화 할 수 있습니까?

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) 

다른 블로그의 최대 TotalComments가 포함 된 5 개의 게시물이 필요합니다.

UPD. 만약 내가 제대로 이해하고 SQL 서버,하지만 난 postid 고유 표준 SQL

Answer 1

을 선호하는, 그래서 이것은

이

편집 도움이 될 것입니다 다음

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 

당신은있을 수 있습니다

확인이 시도 여러 개의 최대 blog-totalComments 조합.

Answer 2

이 당신에게 블로그 당 최고 포스트 줄 것이다 : 또는

SELECT * FROM (
    SELECT *, Ranking = ROW_NUMBER() OVER (PARTITION BY BlogID ORDER BY TotalComments DESC) 
    FROM BlogPosts 
) a 
WHERE Ranking = 1 

:

SELECT b.* 
FROM (
    SELECT DISTINCT BlogID 
    FROM BlogPosts 
) a 
CROSS APPLY (
    SELECT TOP 1 b.* FROM BlogPosts b 
    WHERE a.BlogID = b.BlogID 
    ORDER BY b.TotalComments DESC 
) b 

은 당신이 찾고있는 무엇인가요?

Answer 3

왜 조인과 하위 쿼리가 필요합니까? 왜 쓸 수 없습니까?

SELECT TOP 5 * 
FROM @BlogPosts bp order by TotalComments desc;