<?php
$db = new Mysqli('localhost', 'dbaseuser', 'password');
$db->select_db("ascent");

$query = "SELECT entryid, SUM(percentchance) AS calc
		  FROM loot_fishing
		  GROUP BY entryid";

$result = $db->query($query);

$ii=0;
while ($t_row = $result->fetch_assoc()) {
	$calcData[$ii]["entryid"] = $t_row["entryid"];
	$calcData[$ii]["calc"] = $t_row["calc"];
	$ii++;
}


foreach ($calcData AS $key => $value) {
	$query = "UPDATE loot_fishing
			  SET percentchance = percentchance/" . $value['calc'] . "
			  WHERE entryid = " . $value['entryid'];
	$db->query($query);

}
?>