從連接表中僅獲取 3 行

Question

我試圖從連接表中只獲取三行。 例如，我有一個類別表。 我想在不使用 SQL 內部循環的情況下從這些類別中獲取流行類別和 3 篇文章。 總帖子數應為 12。

我試過這個，但沒有用。 （如果我設置limit 1就可以了。但不能在limit 3上工作）

SELECT 
    categories.name AS cname,
    categories.url  AS curl,
    articles.name,
    articles.url,
    articles.image
FROM   
    categories
    JOIN articles ON articles.id = (
        SELECT p.id
        FROM articles AS p
        WHERE categories.id = p.category AND p.delete = '0'
        ORDER  BY p.id DESC
        LIMIT  3
    )
WHERE  
    categories.delete = '0'
    AND categories.popular = '1'

Answer 1

您的子查詢返回多條記錄（實際上是 3 條），因此應將相等運算符替換為IN運算符。

考慮：

SELECT 
    categories.name AS cname,
    categories.url  AS curl,
    articles.name,
    articles.url,
    articles.image
FROM   
    categories
    JOIN articles ON articles.id IN (
        SELECT p.id
        FROM articles AS p
        WHERE categories.id = p.category AND p.delete = '0'
        ORDER  BY p.id DESC
        LIMIT  3
    )
WHERE  
    categories.delete = '0'
    AND categories.popular = '1'

Answer 2

在 MySQL 8+ 中，您只需執行以下操作：

SELECT c.name AS cname, c.url  AS curl,
       a.name, a.url, a.image
FROM categories c JOIN
     (SELECT a.*,
             ROW_NUMBER() OVER (PARTITION BY a.category ORDER BY a.id DESC) as seqnum
      FROM articles a
      WHERE a.delete = 0
     ) a
     ON a.category = c.id
WHERE a.seqnum <= 3 AND
      c.delete = 0 AND
      c.popular = 1