Check if <input> is empty or only whitespace - mysql

Question

Some website's search boxes aren't very good: when you put a space in the search bar and submit, it returns every search item they have. (Example: http://watchfreemovies.unblocked.co/)
Mine does the same. What can I do to make it verify that there is actual text in the search box before submitting?
Search box and button:
<div class="Nava">
<input type="button" name="button" id="hello" value="M" />
</div>
<form action='/search.php' method='GET'>
<input id='searchbar' type='text' name='search' placeholder="search for movies & shows" maxlength="50" />
<input id='submit' type='submit' name='submit' value='Search' />
</form>
<div class="Navbuttons">
<input type="button" name="button" id="button" value="shows" />
<input type="button" name="button" id="button" value="movies" />
</div>
Results page:
$x = 0;
$construct = '';
$search = $_GET['search'];
$search = preg_replace("#[^0-9a-z ]#i", "", $search);
if (strlen($search) <= 0)
echo "Search term too short";
else {
echo "You searched for '<b>$search</b>' ";
mysql_connect("localhost", "root", "");
mysql_select_db("search");
$search_exploded = explode(" ", $search);
foreach ($search_exploded as $search_each) {
$x++;
if ($x == 1)
$construct .= "keywords LIKE '%$search_each%'";
else
$construct .= "AND keywords LIKE '%$search_each%'";
}
$construct = "SELECT * FROM searchengine WHERE $construct";
$run = mysql_query($construct);
$foundnum = mysql_num_rows($run);
if ($foundnum == 0)
echo "<p>Sorry, there are no matching result for '<b>$search</b>'.</p>
<li> Try different words with similar
meaning</li>
<li> make sure you're spelling is correct</li>";
else {
echo "$foundnum results found !";
while ($runrows = mysql_fetch_assoc($run)) {
$title = $runrows['title'];
$desc = $runrows['description'];
$url = $runrows['url'];
echo "
<hr><a href='$url'><h2><b>$title</b></h2></a><br>
$desc<br>
<a href='$url'></a><p>
";
}
}
}

Answer 1

Check server-side:
if (!trim($_GET['search'])) {
echo 'Enter a query.';
}
Check client-side:
<form action='/search.php' method='GET'>
<input id='searchbar' type='text' name='search' placeholder="search for movies & shows" maxlength="50" required />
<input id='submit' type='submit' name='submit' value='Search' disabled />
</form>
<script>
document.getElementById('searchbar').onkeypress = function() {
document.getElementById('submit').disabled = !this.value.trim();
}
</script>
Fiddle