MySQL查詢來獲得最後一個記錄在每個類別

Question

我有兩個表：文章和類別（約20種），我想獲得最新的10篇文章，但不超過一個從類別。

表文章

id | title | text 

表分類

id | name 

表ArticlesCategories

article | category 

（文章和類別之間relationsl表）

即時通訊使用下面的查詢，但問題是，10個結果並不是所有的最新文章。

SELECT id, title, categoryId, categoryName 
FROM ( 
     SELECT a.id, a.title, ac.category AS categoryId, c.name AS categoryName 
     FROM articles AS a 
      LEFT JOIN articles_categories AS ac ON ac.article = a.id 
      LEFT JOIN categories AS c ON c.id = ac.category 
     WHERE ac.priority = 1 
     ORDER BY a.id DESC) AS tmp_table 
GROUP BY categoryId LIMIT 10 

Answer 1

添加ORDER BY id DESC到您的查詢

這是獲得最後10行的辦法是顛倒順序，選擇前十行​​：基於什麼

SELECT id, title, categoryId, categoryName 
FROM ( 
     SELECT a.id, a.title, ac.category AS categoryId, c.name AS categoryName 
     FROM articles AS a 
      LEFT JOIN articles_categories AS ac ON ac.article = a.id 
      LEFT JOIN categories AS c ON c.id = ac.category 
     WHERE ac.priority = 1 
     ORDER BY a.id DESC) AS tmp_table 
GROUP BY categoryId ORDER BY id DESC LIMIT 10