Catching the selected option's value

I want to pass a select option value through hyperlink to the next page and for this I have this code:

<!doctype html>
<html lang="en">
<head>
</head>
<body>
<form name="search_form" role="form" method="GET" id="search_form" action="SearchResults.php">
  <?php 
    try {
      $conn = new PDO('sqlite:db/MyDatabase.db');
      $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
      $stmt = $conn->prepare("SELECT * FROM attributes WHERE attributename='mushtype'");
      $stmt->execute();
      $data = $stmt->fetchAll(PDO::FETCH_ASSOC);
  ?>

  <select id="mushtype" name="mushtype">
    <option value="*" selected>Mushroom types</option>
    <?php foreach($data as $row): ?>
        <option value="<?php echo $row['idattributevalue']; ?>"><?php echo $row['attributevalueEN']; ?></option>
    <?php endforeach; ?>
  </select>

  <?php 
    } catch(PDOException $e) {
    echo "Error: " . $e->getMessage();
    }
    $conn = null;
  ?>

  <a href="SearchResults.php?mushtype=<?php echo $row['idattributevalue']?>">Find Your Mushroom</a>

</form>
</body>
</html>

For the default selected option I want to use (*) as value because if no option are selected, will stand as SELECT (all) FROM for my SQL query on the second page. So, i tried to construct my hyperlink, but i don't know how to catch the selected option. I tried to adapt from here

    <?php  
        if(isset($_POST['submit'])){  
        if(!empty($_POST['Movies'])) {  
            $selected = $_POST['Movies'];  
            echo 'You have chosen: ' . $selected;  
        } else {  
            echo 'Please select the value.';  
        }  
        }  
    ?>

but I'm unable to do it. Rigth now, my code inserting a value, but is without any control upon it.

Please help me to catch the selected option and insert it as value in my hyperlink. Thank you.

Solution

When you use <a>, you do not submit the inputs to the next page. Instead of

<a href="SearchResults.php?mushtype=<?php echo $row['idattributevalue']?>">Find Your Mushroom</a>

simply use

<input type="submit" value="Find Your Mushroom">

before closing the form.

Edit: Depending on the <form method= you use ("get" or "post"), you will then either have $_GET['mushtype'] or $_POST['mushtype'] available in the next page. (Thanks to @ADyson!)

In my tests using method="get", the form inputs make their way to $_GET, but my uri parameters were not there. Using method="post" gave me both my uri parameters in $_GET and form details in $_POST, just in case you want to use both.

If you do not like the button style however, you can change it using CSS to look just like a regular hyperlink.