wybierz podobne wartości z bazy mysql

Możesz skorzystać z between MySQL i limit klauzula na to:

$range = 5;  // you'll be selecting around this range. 
$min = $rank - $range;
$max = $rank + $range;
$limit = 10; // max number of results you want. 

$query = "select * from table where rank between $min and $max limit $limit";