mysql 联合查询在数据库里测试时正确，通过php操作就不对了？

SQL语句如下：
"SELECT t.task_name,t.task_begin_p,t.task_end_p,t.task_end_r,p.proj_name from tasks as t inner join projects as p on t.task_project_id=p.proj_id where t.task_user_id=".$_SESSION['user_id']."order by t.task_begin_p ASC,t.task_end_p ASC;"

php代码如下：

$link = mysqli_connect('localhost','root','root');
$db = mysqli_select_db($link,'workon');
mysqli_query($link,"set names 'utf8'"); 
$query = "SELECT t.task_name,t.task_begin_p,t.task_end_p,t.task_end_r,p.proj_name from tasks as t inner join projects as p on t.task_project_id=p.proj_id where t.task_user_id=".$_SESSION['user_id']."order by t.task_begin_p ASC,t.task_end_p ASC";
 $data = mysqli_query($link,$query);
while ($row = mysqli_fetch_assoc($data)) {};

返回错误如下：
Warning: mysqli_fetch_assoc() expects parameter 1 to be mysqli_result, boolean given in

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大神就是大神~~~楼上正解，想评论来着，搞错地方了

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=".$_SESSION['user_id']."order by 这里，看到了吗？order by 前面没空格。