html - PHP - How Insert a variable link (a href) inside other variable value? -

i'm trying away:

<?php    $link = "'index.php?id=echo ['post_id']; "  ?>

<?php  while ($row = mysql_fetch_array($result)) {   echo "<span class='survey-name'><a href='$link'>". $row['title'] ."</span>";  ?>

but when click link refresh page, instead of redirects variable element (), added in db mysql , exposed @ home, clicking on link direct page of details of specific element working, not targeting properly.

function get_posts($id = null, $cat_id = null){      $posts = array();      $query = "select `posts`.`id` `post_id` , `categories`.`id` `category_id`, `title`,`endereco`,`cidade`,`email`,`telefone`,`categories`.`name` `posts` inner join `categories` on `categories`.`id` = `posts`.`cat_id` " ;      if(isset($id)){          $id = (int)$id;          $query .= " `posts`.`id` = {$id} ";               }      if(isset($cat_id)){          $cat_id = (int)$cat_id;          $query .= " `cat_id` = {$cat_id} ";               }                         $query .= "order `post_id` desc";            $query = mysql_query($query);            while($row = mysql_fetch_assoc($query)){      $posts[] = $row;     }     return $posts;  }

in php:

$link = 'index.php?id='.$row['post_id']; print '<span class="survey-name"><a href="'.$link.'">'.$row['title'].'</span>'; 

note: guess ['post_id'] $row['post_id'] because ['post_id'] nothing.