Попробуйте следующее:
<?php
if (isset($_POST['submit'])){
// amount of numbers
$num = $_POST['num'];
// array of different numbers
$num_ar = [];
// infinity loop
for ( ; ; ) {
// random number
$rand1 = rand(1000000, 9999999);
// 14-digits
//$rand1 = rand(10000000000000, 99999999999999);
// if it is a different number
if(!in_array($rand1,$num_ar)) {
$sql = mysql_query("INSERT INTO pins(randi) VALUES('$rand1')";
array_push($num_ar,$rand1);
}
// stop the loop
if (count($num_ar) == $num) break;
}
}
?>
или
<?php
if (isset($_POST['submit'])){
// amount of numbers
$num = $_POST['num'];
// array of different numbers
$num_ar = [];
// while loop
while (count($num_ar) !== $num) {
// random number
$rand1 = rand(1000000, 9999999);
// 14-digits
//$rand1 = rand(10000000000000, 99999999999999);
// if it is a different number
if(!in_array($rand1,$num_ar)) {
$sql = mysql_query("INSERT INTO pins(randi) VALUES('$rand1')";
array_push($num_ar,$rand1);
}
}
}
?>