filter data pdo - php

Question

What I am trying to do is similar to this. Search Filtering with PHP/MySQL
<?php
require 'con.php';
$minage = $_POST['data'][0];
$maxage = $_POST['data'][1];
$gender = $_POST['data'][2];
$religion = $_POST['data'][3];
$query = "SELECT CONCAT(firstname, ' ', middlename, ' ', lastname, ' ', extension_name) as fullname, TIMESTAMPDIFF(YEAR, birthday ,NOW()) as age FROM mytable";
$filter = array();
if($gender != -1){
$gender = substr($gender, 1, -1);
$filter[] = "gender = :gender";
}
if($religion != -1){
$filter[] = "religion = :religion";
}
if(count($filter) > 0){
$query .= " WHERE " . implode(' AND ', $filter);
$sql = $connection->prepare($query);
-> $sql->bindParam(':gender', $gender, PDO::PARAM_STR);
-> $sql->bindParam(':religion', $religion, PDO::PARAM_STR);
$sql->execute();
$res = $sql->fetchAll();
}else{
$sql = $connection->prepare($query);
$sql->execute();
$res = $sql->fetchAll();
}
?>
<?php foreach($res as $row): ?>
<div><?php echo $row['fullname'];?></div>
<?php endforeach; ?>
When I select a gender and religion on my dropdown, the result is fine.
But when I select only one, let's say gender, I received an error:
number of bound variables does not match number of tokens
I'm a bit confused where to place $sql->bindParam(...);. I guess this is the cause of my error? Or if there's more 'error' or if there's anything that's not right, please correct me. Thank you in advance.

Answer 1

Just add value right along with placeholder and then send them right to execute
if($gender != -1){
$filter[] = "gender = ?";
$values[] = $gender;
}
if($religion != -1){
$filter[] = "religion = ?";
$values[] = $religion;
}
$query .= " WHERE 1 AND " . implode(' AND ', $filter);
$stmt = $connection->prepare($query);
$stmt->execute($values);

Answer 2

Bind shoud be conditional also:
if($gender != -1){
$filter[] = "gender = :gender";
}
if($religion != -1){
$filter[] = "religion = :religion";
}
if(count($filter) > 0){
$gender = substr($gender, 1, -1);
$query .= " WHERE " . implode(' AND ', $filter);
$sql = $connection->prepare($query);
if($gender != -1){
$sql->bindParam(':gender', $gender, PDO::PARAM_STR);
}
if($religion != -1){
$sql->bindParam(':religion', $religion, PDO::PARAM_STR);
}
$sql->execute();
$res = $sql->fetchAll();
}else{
thats a very badly organized code, try to make it more readable