Is there a faster way than array_diff in PHP - php

Question

I have a set of numbers from MySQL within the range 1000 0000 (8 digits) to 9 999 999 999 (10 digits). It's supposed to be consecutive, but there are missing numbers. I need to know which numbers are missing.
The range is huge. At first I was going to use PHP to do this:
//MySqli Select Query
$results = $mysqli->query("SELECT `OCLC Number` FROM `MARC Records by Number`");
$n_array = array();
while($row = $results->fetch_assoc()) {
$n_array[] = $row["OCLC Number"];
}
d($n_array);
foreach($n_array as $k => $val) {
print $val . " ";
}
/* 8 digits */
$counter = 10000000;
$master_array = array();
/* 10 digits */
while ($counter <= 9999999999 ) {
$master_array[] = $counter;
$counter++;
d($master_array);
}
d($master_array);
$missing_numbers_ar = array_diff ($master_array, $n_array);
d($missing_numbers_ar);
d() is a custom function akin to var_dump().
However, I just realized it would take tons of time for this to be done. At the 15 minute mark, $master_array is being populated with only 4000 numbers.
How can I do this in a quicker way? MySQL-only or MySQL-and-PHP solutions both welcome. If the optimal solution depends on how many numbers are missing, please let me know how so. Tq.

Answer 1

Your d() probably is the cause of slowness, please remove it, and make small changes in your code
while($row = $results->fetch_assoc()) {
$n_array[$row["OCLC Number"]] = 1;
}
and
$missing_numbers_ar = [];
while ($counter++ <= 9999999999 ) {
if (empty($n_array[$counter])) {
$missing_numbers_ar[] = $counter;
}
}

Answer 2

If the following is still slow I would be surprised. I also just noticed it is similar to #Hieu Vo's answer.
// Make sure the data is returned in order by adding
// an `ORDER BY ...` clause.
$results = $mysqli->query("SELECT `OCLC Number`
FROM `MARC Records by Number`
ORDER BY `OCLC Number`");
$n_array = array();
while($row = $results->fetch_assoc()) {
// Add the "OCLC Number" as a key to the array.
$n_array[$row["OCLC Number"]] = $row["OCLC Number"];
}
// assume the first array key is in fact correct
$i = key($n_array);
// get the last key, also assume it is not missing.
end($n_array);
$max = key($n_array);
// reset the array (should not be needed)
reset($n_array);
do {
if (! $n_array[$i]) {
echo 'Missing key:['.$i.']<br />';
// flush the data to the page as you go.
flush();
}
} while(++$i <= $max);