Although the documentation says you must provide a number between 0 and count - 1, you can actually supply a negative number, which appears to be cast to positive (such as in abs()).
For example:
<?php
$db = new mysqli('localhost', 'test', 'password', 'schema');
$db->multi_query("
SELECT * FROM
(
SELECT 1 as 'position'
UNION SELECT 2 as 'position'
UNION SELECT 3 as 'position'
UNION SELECT 4 as 'position'
UNION SELECT 5 as 'position'
) as rows");
$result = $db->store_result();
for ($i = 0; $i < $result->num_rows; $i++)
{
$offset = $i;
$result->data_seek($offset);
var_dump("Seek offset is: {$offset}", $result->fetch_object());
}
for ($i = 0; $i < $result->num_rows; $i++)
{
$offset = -$i;
$result->data_seek($offset);
var_dump("Seek offset is: {$offset}", $result->fetch_object());
}
