php - mysql 返回每个 user_id 的总行数

Question

  $sql = "SELECT * FROM books LEFT JOIN users
           ON books.readby=users.user_id WHERE users.email IS NOT NULL";
  $result = mysql_query($sql);
  while($row = mysql_fetch_array($result))
     {
echo $row['readby']. " - read 10 books";
 } //while ends

这是我目前的代码。我正在尝试检索每个用户阅读的书籍数量并回应结果。 echo user_id 和他/她读过的书的数量books 表是这样的:id - name - pages - readbyreadby 行包含用户 ID。有什么想法/建议吗？我正在考虑使用 count()，但我不确定该怎么做。

Answer 1

子查询可以返回每个用户阅读的书籍数量。这是与主表左连接以检索关于每个用户的其他列。

编辑 GROUP BY 已被省略...

SELECT 
  users.*,
  usersread.numread
FROM 
  users
  /* join all user details against count of books read */
  LEFT JOIN  (
    /* Retrieve user_id (via readby) and count from the books table */
    SELECT 
      readby,
      COUNT(*) AS numread
    FROM  books
    GROUP BY readby
  ) usersread ON users.user_id = usersread.readby

然后在您的 PHP 中，您可以在获取结果后检索 $row['numread']。

// Assuming you already executed the query above and checked errors...
while($row = mysql_fetch_array($result))
{
  // don't know the contents of your users table, but assuming there's a 
  // users.name column I used 'name' here...
  echo "{$row['name']} read {$row['numread']} books.";
}