test892.php

<?php
$units = array(3, 8, 4, 5);
$cn = 0;
$units = array_map(function($a) use(&$cn) {
  $cn++;
  return array($a, $cn);
}, $units);
$first = array_shift($units);
$s = array_reduce($units, function($res, $item) {
  return $res." UNION SELECT ".$item[0].", ".$item[1]." ";
}, "SELECT ".$first[0]." AS id, ".$first[1]." AS uorder ");

$sql = "
SELECT a.id, u.unitName, m.moduleName 
FROM ($s) a 
LEFT JOIN modules m ON m.unid=a.id 
LEFT JOIN units u ON u.id=m.unid 
ORDER BY a.uorder;\n";
echo $sql;
?>