如何计算while循环内查询的行数？

Question

我有以下PHP代码

$thread_pick=mysqli_query($db,'SELECT * FROM u_mess WHERE participant_1="'.$display_name.'" OR participant_2="'.$display_name.'" ') or trigger_error(mysqli_error());
if(mysqli_num_rows($thread_pick) >= 1 )
{
  while($row = mysqli_fetch_assoc($thread_pick))
  {
    $thread_pick_sub = mysqli_query($db,'SELECT * FROM u_mess_thread WHERE (thread_id="'.$row['thread_id'].'" AND mess_to="'.$display_name.'" )')or trigger_error(mysqli_error());
    echo mysqli_num_rows($thread_pick_sub).'dsddsds';
    $mess_num_count = mysqli_num_rows($thread_pick_sub);
  }
}

我的问题：该表有两个用户，用户1发送了3条消息，用户2发送了2条消息，现在变量$mess_num_count内的$mess_num_count应为5，但它显示2我该怎么做才能使其正常工作

Answer 1

我认为这只是计算来自user 2的消息，所以它是2 ！

要获得5您必须使用运算符+=如下所示：

$mess_num_count += mysqli_num_rows($thread_pick_sub);

然后，代码应如下所示：

$thread_pick=mysqli_query($db,'SELECT * FROM u_mess WHERE participant_1="'.$display_name.'" OR participant_2="'.$display_name.'" ') or trigger_error(mysqli_error());
$mess_num_count = 0;
if(mysqli_num_rows($thread_pick) >= 1 )
{
  while($row = mysqli_fetch_assoc($thread_pick))
  {
    $thread_pick_sub = mysqli_query($db,'SELECT * FROM u_mess_thread WHERE (thread_id="'.$row['thread_id'].'" AND mess_to="'.$display_name.'" )')or trigger_error(mysqli_error());
    echo mysqli_num_rows($thread_pick_sub).'dsddsds';
    $mess_num_count += mysqli_num_rows($thread_pick_sub);
  }
}