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

这是我到目前为止的代码。我正在尝试检索每个用户读取的书籍数量并回应结果。回显user_id和他/她阅读的书籍数量 books表是这样的：id - name - pages - readby 行readby包含用户id.any想法/建议？我在考虑使用count（），但我不知道该怎么做。

Answer 1

您可以这样使用count()：

<?php
    $count = mysql_fetch_array(mysql_query("SELECT COUNT(`user_id`) FROM books LEFT JOIN users ON books.readby=users.user_id WHERE users.email IS NOT NULL GROUP BY `user_id`"));
    $count = $count[0];
?>

希望这有帮助！：）

Answer 2

子查询可以返回每个用户读取的书籍数。这是左连接主表，以检索有关每个用户的其他列。

修改 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

在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.";
}

mysql返回每个user_id的总行数

2 个答案: