Xin giúp đỡ câu lệnh SELECT

Question

SQL fiddle : http://sqlfiddle.com/#!9/5a3e95/2

Accepted Answer

Câu hỏi ko rõ nghĩa lắm, nên có gì bạn tự chỉnh lại nhé. Đây là query select 2 comment mới nhất của mỗi post

```sql
SELECT p.id,
       p.content,
       c.comment,
       c.user_id,
       c.date_created
  FROM (
        
        SELECT c.post_id,
                c.comment,
                c.date_created,
                c.user_id,
                COUNT(*) AS row_number
          FROM comments c        
         INNER JOIN comments c2
            ON c.post_id = c2.post_id
              
           AND c.date_created <= c2.date_created
        
         GROUP BY c.post_id,
                   c.date_created,
                   c.comment,
                   c.user_id
        
        ) c
 INNER JOIN posts p
    ON p.id = c.post_id

WHERE c.row_number <= 2
```

Answer

Nếu cần thêm nội dung comment thì comments trong group thành 1 added fields array object dạng json string
```sql
SELECT posts.id as post_id, users.username as publisher_username, users.id as publisher_id, 
SUBSTRING_INDEX( GROUP_CONCAT(comments.id ORDER BY comments.date_created DESC), &#x27;,&#x27;, 2) comment_ids 
FROM posts
LEFT JOIN comments ON posts.id = comments.post_id
LEFT JOIN users ON users.id = posts.user_id
GROUP BY posts.id
```

2 CÂU TRẢ LỜI