如何從SQL中的各個連接到同一個表中計數？

Question

我有兩張表，博客和文章，以及他們之間的預期關係。帖子可以發佈或起草。我想選擇所有發佈和發佈帖子數量的博客。我該怎麼做？

我嘗試此查詢：

SELECT blogs.*, 
     COUNT(published_posts.*) AS published_post_count, 
     COUNT(draft_posts.*) AS draft_post_count 
FROM blogs 
JOIN posts AS published_posts ON published_posts.blog_id=blogs.id AND 
           published_posts.state = "published" 
JOIN posts AS draft_posts ON draft_posts.blog_id=blogs.id AND 
          draft_posts.state = "draft" 
GROUP BY blogs.id 

但我結束了兩個published_post_count和draft_post_count和犯錯兩個相同的號碼。

然後我變得絕望和特里：

SELECT blogs.*, 
     COUNT(published_posts.*) AS published_post_count, 
     COUNT(draft_posts.*) AS draft_post_count 
FROM blogs 
JOIN (SELECT * FROM posts WHERE posts.state="published") AS published_posts 
    ON published_posts.blog_id=blogs.id 
JOIN (SELECT * FROM posts WHERE posts.state="draft") AS draft_posts 
    ON draft_posts.blog_id=blogs.id 
GROUP BY blogs.id 

但在這兩種情況下，我有同樣的錯誤的結果。

這樣做的正確方法是什麼？

謝謝。

Answer 1

如果您只是對COUNT感興趣，而您也是JOIN的表格。所以必須有一個或多個post已經published和一個或多個draft。因此，也許這將幫助你：

SELECT blogs.*, 
     (
      SELECT COUNT(*) 
      FROM posts 
      WHERE posts.blog_id=blogs.id 
      AND posts.state = "published" 
     ) AS published_post_count, 
     (
      SELECT COUNT(*) 
      FROM posts 
      WHERE posts.blog_id=blogs.id 
      AND posts.state = "draft" 
     ) AS draft_post_count, 
FROM blogs 

Answer 2

嘗試：

GROUP BY blogs.id,published_posts.[theKeyOfThisTable],draft_posts.[theKeyOfThisTable] 

，你應該包含的「選擇」在你列「GROUP BY」子句

Answer 3

你也許可以算不同狀態並回到博客：

SELECT blogs.*, p.published_post_count, p.draft_post_count 
FROM blogs 
JOIN 
(
    SELECT posts.blog_id, 
     SUM(case when posts.state = 'published' then 1 end) 
      AS published_post_count, 
     SUM(case when posts.state = 'draft' then 1 end) 
      AS draft_post_count 
    FROM posts 
    GROUP BY blog_id 
) p 
ON p.blog_id=blogs.id