<?php
// THERE IS ABSOLUTELY NO WARRANTY ON THIS SCRIPT! YOU ARE USING THIS ON YOUR
// OWN RISK!

$link = mysql_connect("localhost", "user", "password") or die(mysql_error());
$db = mysql_select_db("dbname", $link) or die(mysql_error($link));

$err = "false"; $total = 0;
while (!empty($err)) {
	echo "Trying ALTER TABLE... ";
	$alter = @mysql_query("ALTER TABLE `wp_post2tag` ADD UNIQUE (`tag_id` , `post_id`)");
	flush();
	echo "done.\n";
	flush();
	$err = mysql_error($link);
	if (!empty($err)) {
		// Analyse the error message
		$data = explode(" ", $err);
		$data = substr($data[2], 1, -1);
		$data = explode("-", $data);
		echo "Searching for entries...";
		$query = @mysql_query(sprintf("SELECT COUNT(tag_id) FROM wp_post2tag WHERE tag_id = '%s' AND post_id = '%s'",
			mysql_real_escape_string($data[0]), mysql_real_escape_string($data[1]))) or die(mysql_error($link));
		flush();
		list($rows) = mysql_fetch_row($query);
		echo "done.\n";
		flush();
		$rows--;
		if ( $rows > 0 ) {
			echo "Deleting ".number_format($rows)." for post_id=".$data[0]." ...";
			$query = mysql_query(sprintf("DELETE FROM wp_post2tag WHERE tag_id = '%s' AND post_id = '%s' LIMIT %s",
				mysql_real_escape_string($data[0]), mysql_real_escape_string($data[1]), $rows)) or die(mysql_error($link));
			echo "done.\n";
			flush();
			$total += $rows;
		}
	}
}

echo "Total lines deleted: ".number_format($total);
mysql_close($link);

?>