<?php

$data = <<<DATA
<html>
<head/>
<body>
	<table id="two_rows">
		<tr><td>One column</td></tr>
		<tr><td>Another column</td></tr>
	</table>

	<table id="one_row">
		<tr><td>One column</td></tr>
	</table>
</body>
</html>
DATA;

$dom = new DOMDocument();
$dom->loadHTML($data);

$xpath = new DOMXPath($dom);
$tables = $xpath->query("//table[count(tr) = 1]");
print_r($tables);
?>