I am having a problem getting data from a large amount MySQL database.
With the below code it is ok to get the list of 10K patients and 5K appointments which is our test server.
However, on our live server, the number of patients is over 100K and the number of appointments is over 300K and when I run the code after a while it gives 500 error.
I need the list of the patients whose patient_treatment_status is 1 or 3 and has no appointment after one month from their last appointment. (The below code is working for small amount of patients and appointments)
How can I optimise the first database query so there will be no need the second database query in the foreach loop?
<?php
ini_set('memory_limit', '-1');
ini_set('max_execution_time', 0);
require_once('Db.class.php');
$patients = $db->query("
SELECT
p.id, p.first_name, p.last_name, p.phone, p.mobile,
LatestApp.lastAppDate
FROM
patients p
LEFT JOIN (SELECT patient_id, MAX(start_date) AS lastAppDate FROM appointments WHERE appointment_status = 4) LatestApp ON p.id = LatestApp.patient_id
WHERE
p.patient_treatment_status = 1 OR p.patient_treatment_status = 3
ORDER BY
p.id
");
foreach ($patients as $row) {
$one_month_after_the_last_appointment = date('Y-m-d', strtotime($row['lastAppDate'] . " +1 month"));
$appointment_check = $db->single("SELECT COUNT(id) FROM appointments WHERE patient_id = :pid AND appointment_status = :a0 AND (start_date >= :a1 AND start_date <= :a2)", array("pid"=>"{$row['id']}","a0"=>"1","a1"=>"{$row['lastAppDate']}","a2"=>"$one_month_after_the_last_appointment"));
if($appointment_check == 0){
echo $patient_id = $row['id'].' - '.$row['lastAppDate'].' - '.$one_month_after_the_last_appointment. '<br>';
}
}
?>