限制在我的 sql 查询中不起作用答案

【问题标题】：limit not working in my sql query限制在我的 sql 查询中不起作用
【发布时间】：2013-09-10 09:16:27
【问题描述】：

我在 php.ini 中创建了一个“你可能认识的人”脚本。这个脚本向我展示了我朋友的朋友，在一个 php 朋友系统中。我有一个名为 users (user_id, name, surname, email, profile) 的表，其中包含有关用户的信息。另一个名为 friends(friend_id, user_one, user_two) 的表保存了好友用户的 ID。我的代码如下：

<?php

//----- get friends of friends -------


$friends_of_friends = mysql_query(" SELECT u.*
FROM (SELECT DISTINCT user_one as user_id
        FROM friends
        WHERE user_two IN (SELECT user_one as user_id
                  FROM friends
                  WHERE user_two = '$session_user_id'
                  UNION DISTINCT
                  SELECT user_two
                  FROM friends
                  WHERE user_one = '$session_user_id')
        UNION DISTINCT
    SELECT DISTINCT user_two
        FROM friends
        WHERE user_one IN (SELECT user_one as user_id
              FROM friends
                  WHERE user_two = '$session_user_id'
                  UNION DISTINCT
              SELECT user_two
              FROM friends
              WHERE user_one = '$session_user_id')
     ) f
 JOIN users u
 ON u.user_id = f.user_id  ");


  while ($run_friends= mysql_fetch_assoc($friends_of_friends)) {

  $friend_friend_id = $run_friends['user_id'];  



// ---- friends of my friends that are not my friends --------------


$check_friend_query = mysql_query("  SELECT friends_id from friends WHERE  (user_one='$session_user_id' AND user_two='$friend_friend_id') OR (user_one='$friend_friend_id' AND user_two='$session_user_id')   ");

if (mysql_num_rows($check_friend_query) != 1){ 

    $not_friends = mysql_query("SELECT `user_id`, `name`, `surname`, `email`, `profile` FROM `users` WHERE (`user_id`='$friend_friend_id' AND `user_id`!='$session_user_id')  "); 



    while ($run_not_friends= mysql_fetch_assoc($not_friends)) {
      $i=1;
    if ($i <= 3)
    {                                                           
    $not_friend_id = $run_not_friends['user_id'];

                  echo $not_friend_id;

     $i++;
     }
    }

  }//end if

 }//end while

?>

一切正常。我想要的只是选择并显示 3 个人，他们是我朋友的朋友（因为我可能有一个列表很多人是我朋友的朋友）。如您所见，我在我的 sql 查询中使用了 LIMIT，但它不起作用。有什么想法吗？

【问题讨论】：

尝试将 LIMIT 3 更改为 LIMIT 0,3
$not_friends = mysql_query("SELECT user_id, name, surname, email, profile FROM users WHERE (user_id='$friend_friend_id' AND @ 987654329@!='$session_user_id') 限制 3;"); - 它只会返回一行。这里的限制是没有用的
好的..知道在哪里设置限制吗？
@user2491321> 建议：不要多次使用这样的查询，因为那样会对服务器造成压力。
你是对的......你还有什么想法吗？

标签： php mysql

【解决方案1】：

试试这个代码。将打印 3 个朋友 ID。我没试过。

$i=1;
while ($run_friends= mysql_fetch_assoc($friends_of_friends)) {

     $friend_friend_id = $run_friends['user_id'];  
     // ---- friends of my friends that are not my friends --------------

     if ($i <= 3)
     { 
          $check_friend_query = mysql_query("  SELECT friends_id from friends WHERE  (user_one='$session_user_id' AND user_two='$friend_friend_id') OR (user_one='$friend_friend_id' AND user_two='$session_user_id')   ");

          if (mysql_num_rows($check_friend_query) != 1){ 
              $not_friends = mysql_query("SELECT `user_id`, `name`, `surname`, `email`, `profile` FROM `users` WHERE (`user_id`='$friend_friend_id' AND `user_id`!='$session_user_id')  ");
               while ($run_not_friends= mysql_fetch_assoc($not_friends)) {
                   $not_friend_id = $run_not_friends['user_id'];
                   echo $not_friend_id;
                   $i++;
               }
          }//end if
      }
 }//end while

【讨论】：

感谢您的回答，但仍将它们全部打印...如果我将 3 更改为 2 或 1 仍将它们全部打印。如果我将 3 更改为 0，则不打印任何内容
我完全按照你给我的方法做了，但是没有结果，仍然打印出来。
你在 while 循环之前给出了 if ($i
让我们continue this discussion in chat

【解决方案2】：

试试这个：

<?php

//----- get friends of friends -------


$friends_of_friends = mysql_query(" SELECT u.*
FROM (SELECT DISTINCT user_one as user_id
        FROM friends
        WHERE user_two IN (SELECT user_one as user_id
                  FROM friends
                  WHERE user_two = '$session_user_id'
                  UNION DISTINCT
                  SELECT user_two
                  FROM friends
                  WHERE user_one = '$session_user_id')
        UNION DISTINCT
    SELECT DISTINCT user_two
        FROM friends
        WHERE user_one IN (SELECT user_one as user_id
              FROM friends
                  WHERE user_two = '$session_user_id'
                  UNION DISTINCT
              SELECT user_two
              FROM friends
              WHERE user_one = '$session_user_id')
     ) f
 JOIN users u
 ON u.user_id = f.user_id  ");


  while ($run_friends= mysql_fetch_assoc($friends_of_friends)) {

  $friend_friend_id = $run_friends['user_id'];  



// ---- friends of my friends that are not my friends --------------


$check_friend_query = mysql_query("  SELECT friends_id from friends WHERE  (user_one='$session_user_id' AND user_two='$friend_friend_id') OR (user_one='$friend_friend_id' AND user_two='$session_user_id')   ");

if (mysql_num_rows($check_friend_query) != 1){ 

    $not_friends = mysql_query("SELECT `user_id`, `name`, `surname`, `email`, `profile` FROM `users` WHERE `user_id`='$friend_friend_id' AND `user_id`!='$session_user_id' LIMIT 3"); 

    while ($run_not_friends= mysql_fetch_assoc($not_friends)) {

    $not_friend_id = $run_not_friends['user_id'];

                  echo $not_friend_id;
    }

  }//end if

 }//end while

?>

【讨论】：