需要一个可以过滤结果的 MySQL 查询

Question

这里，chapter_id 可以是两个或两个以上。我需要以一种方式查询，每章都给出相等的输出。问题。

即如果总题是 50 题，分 5 章，那么每章应该给出 10 题。

SELECT id, chapter_id, question, answer FROM `questions`
WHERE `chapter_id` IN (19, 20, 21, 22, 23)
ORDER BY `chapter_id`

我通过查询单独的查询进行了尝试。即首先检查章节数并通过数组循环。

<?php
  $total_qsn = 50;
  $chap[] = {19, 20, 21, 22, 23};
  $avg = $total_qsn/count($chap);
  for($i=0, $i<count($chap); i++){
      $sql = "SELECT id, chapter_id, question, answer FROM `questions` WHERE chapter_id = {$chap[i]} LIMIT 0, {$avg}";
      $result = mysql_query($sql);
      while($row = mysql_fetch_assoc($result)){
          // Print the array members
      }
  }
?>

有没有什么办法，我可以通过一个查询来完成整个事情！谢谢！请有任何想法！

Answer 1

试试这个：

SELECT id, chapter_id, question, answer 
FROM (SELECT IF(@chapterId=@chapterId:=chapter_id, @id:=@id+1, @id:=0) queNo, id, chapter_id, question, answer 
      FROM `questions`, (SELECT @chapterId:=0, @id:=0) AS A 
      WHERE `chapter_id` IN (19, 20, 21, 22, 23)
      ORDER BY `chapter_id`
     ) AS A 
WHERE queNo < 10