Where clause if null show all, if where = $variable show $variable - php

Question

I'm a bit stuck on a bit of code im doing.
Here's the code i already have
HTML code:
<form method="post" action="index.php" >
<select name="sortby" class="sortby" >
<option value=" ORDER BY id DESC">Date Added (Newest First)</option>
<option value=" ORDER BY id ASC">Date Added (Oldest First)</option>
<option value="ORDER BY clicks DESC">Website Clicks </option>
<input type="submit" value="Submit" />
</select>
</form>
<form method="post" action="index.php">
<select name="country" class="sortby">
<option value="">Country...</option>
<option value="AF">Afghanistan</option>
<option value="AL">Albania</option>
<option value="DZ">Algeria</option>
<option value="AS">American Samoa</option>
<option value="AD">Andorra</option>
.... and so on
</select>
<input type="submit" value="Submit" />
PHP code:
$sortby = $_POST['sortby'];
$sortby = $mysqli->real_escape_string($sortby);
$country = $_POST ['country'];
$country = $mysqli->real_escape_string($country);
$results = $mysqli->query("SELECT id, link, image, title, description, country, clicks FROM isc_links WHERE approved=1 $sortby");
while($row = $results->fetch_assoc()) {
print '<div id="linkmainwrapper"><div id="linkwrapper"><div class="linkimageborder"><div class="linkimage">'.$row["image"].'</div></div>';
print '<div class="linktitle">'.$row["title"].'</div>';
print '<div class="link">('.$row["link"].')</div>';
print '<div class="countryflag"><img src="http://www.hatblocksdirect.co.uk/lib/flags/'.$row["country"].'.gif"></div>';
print '<div class="linkdescription">'.$row["description"].'</div>';
print '<div class="clickcount">Website Clicks ('.$row["clicks"].')</div></div></div>';
what i would like to do is sort colums. the first sort box works, i can sort by website clicks, id etc using $sortby.
Ive passed the $country using a select drop down but i dont know how to implement this into my select query. I need it to display all entries if a country hasn't been selected. once a country is selected only display that country.
Any help very much appreciated

Answer 1

Put the additional condition of the WHERE clause in a variable depending on whether the parameter is supplied.
if (!empty($_POST['country'])) {
$country = "AND country = '" . $mysqli->real_escape_string($country) . "'";
} else {
$country = "";
}
$results = $mysqli->query("SELECT id, link, image, title, description, country, clicks FROM isc_links WHERE approved=1 $country $sortby");

Answer 2

Use an if condition like
if(isset($_POST ['country']))
{ // if country is set
$country = $mysqli->real_escape_string($_POST ['country']);
$sql="SELECT id, link, image, title, description, country, clicks FROM isc_links WHERE approved=1 and country='$country' $sortby";
}
else
{ // if country is not se
$sql="SELECT id, link, image, title, description, country, clicks FROM isc_links WHERE approved=1 $sortby";
}
$results = $mysqli->query($sql); // execute the query