While doesnt give me more trainers - php

Question

I'm trying to make a map with available gyms that also shows what exercises they have. So it looks like this:
Name Gym
Open spots: (number)
Logo image of Gym
Time of excercise.
Image of a dumbel for example
Trainer
The part from Time of exercise til Trainer needs to show more than one, I got like 6 exercises with 6 trainers, and 6 times and 6 different images of exercises to show. I store those in a database; but they don't show up.
Here my code:
$sql = "SELECT * FROM forts";
$result = $mysqli->query($sql);
if ($result->num_rows > 0) {
echo "[";
$output = array();
while($row = $result->fetch_assoc()) {
$url = preg_replace("/^http:/i", "https:", $row['url']);
$sqlmon = "SELECT * FROM gym_trainers WHERE fort_id = " . $row['id'];
$resultmon = $mysqli->query($sqlmon);
$mon = $resultmon->fetch_assoc();
$sqlextra = "SELECT * FROM extrainfo WHERE fort_id = " . $row['id'] . " ORDER BY last_modified DESC";
$resultextra = $mysqli->query($sqlextra);
$extra = $resultextra->fetch_assoc();
array_push($output, '
{
"id": "' . $row['id'] . '",
"name": "' . htmlspecialchars($row['name']) . '",
"image": "' . $url . '",
"team": "' . $team . '",
"spots": ' . $extra['spots'] . ',
"exer_time": ' . $mon['time_exerise'] . ',
"trainer": "' . htmlspecialchars($mon['trainer_name']) . '",
"exercise_id": ' . $mon['exercise_id'] . ',
"lat": ' . $row['lat'] . ',
"lng": ' . $row['lon'] . '
}
');
}
echo implode(",", $output);
echo "]";
I think something with this part needs to change, but don't know what:
"exer_time": ' . $mon['time_exerise'] . ',
"trainer": "' . htmlspecialchars($mon['trainer_name']) . '",
"exercise_id": ' . $mon['exercise_id'] . ',

Answer 1

The specific problem is that you fetch only 1 record from the gym_trainers table (the $resultmon->fetch_assoc() is not in a separate loop).
The wider problem is that you do not use joins. The 3 separate sql queries could be written as
select *
from forts f
left join gym_trainers g on f.id=g.fort_id
left join extrainfo e on f.id=g.fort_id
In this case you would need a single loop and within the single loop you track if the fort changes.