PHP - How to insert a variable link into a variable href?

Question

I’m trying this way:

<?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 clicking on the link it only gives a refresh on the page, and does not direct to the page of the variable element in question (), which is added by DB mysql and exposed at home, but when clicking on the link I would like you to direct to the details page of this specific element that is already working, just not directing correctly.

SQL:

CREATE TABLE IF NOT EXISTS `categories` (
  `id` int(3) NOT NULL,
  `name` text COLLATE utf8_bin NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

CREATE TABLE IF NOT EXISTS `posts` (
  `id` int(6) NOT NULL,
  `cat_id` int(3) NOT NULL,
  `title` varchar(255) COLLATE utf8_bin NOT NULL,
  `endereco` text COLLATE utf8_bin NOT NULL,
  `cidade` text COLLATE utf8_bin NOT NULL,
  `email` text COLLATE utf8_bin NOT NULL,
  `telefone` text COLLATE utf8_bin NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=24 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

function get_posts($id = null, $cat_id = null){
    $posts = array();
    $query = "SELECT `posts`.`id` AS `post_id` , `categories`.`id` AS `category_id`, `title`,`endereco`,`cidade`,`email`,`telefone`,`categories`.`name` FROM `posts` INNER JOIN `categories` ON `categories`.`id` = `posts`.`cat_id` " ;
    if(isset($id)){
        $id = (int)$id;
        $query .= " WHERE `posts`.`id` = {$id} ";
             }
    if(isset($cat_id)){
        $cat_id = (int)$cat_id;
        $query .= " WHERE `cat_id` = {$cat_id} ";
             }         
        
    $query .= "ORDER BY `post_id` DESC";
    
    $query = mysql_query($query);
    
    while($row = mysql_fetch_assoc($query)){
    $posts[] = $row;
   }
   return $posts;
}

Answer 1

It seems that something is missing in the definition of the link, first set the variable correctly, I believe it is $row and not just [post_id] and finally prints with echo the value contained in $link.

<?php
   $posts = get_posts(); 

   $pagina = 'index.php?id=';
   $formato = "<span class='survey-name'><a href='%s%d'>%s</span>";

   foreach($post as $link){
      printf($formato, $pagina, $link['post_id'], $link['title']);
   }

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