How to combine 2 different filters - php

Question

I created this simple filter for date interval, and different levels (0,1,2). I have this code so far:
if(isset($_POST['filtersubmit'])){
$datex = str_replace('/', '-', $_POST['firstdate']);
$date1 = date("Y-m-d", strtotime($datex));
$datey = str_replace('/', '-', $_POST['lastdate']);
$date2 = date("Y-m-d", strtotime($datey));
$projects = $_POST['projekt'];
if(isset($date1) && isset($date2)){
$query = mysqli_query($conn, "SELECT * FROM zapasy WHERE datum BETWEEN
'$date1' AND '$date2' ORDER BY id DESC");
}
if($projects == 0){
$query = mysqli_query($conn, "SELECT * FROM zapasy WHERE projekt = '0' ORDER BY id DESC") or die(mysqli_errno($conn). '-'. mysqli_error($conn));
} elseif($projects == 1){
$query = mysqli_query($conn, "SELECT * FROM zapasy WHERE projekt = '1' ORDER BY id DESC") or die(mysqli_errno($conn). '-'. mysqli_error($conn));
} elseif($projects == 2){
$query = mysqli_query($conn, "SELECT * FROM zapasy WHERE projekt = '2' ORDER BY id DESC") or die(mysqli_errno($conn). '-'. mysqli_error($conn));
}
}
Now if I select just one of these filters, it works good, but if I want both interval and level filters, it doesn't work. I am not really sure how to do it. I am really grateful for any help.

Answer 1

I would use something along these lines, using a prepared statement to protect you from SQL injection. Basically we form arrays of WHERE clauses, parameters and parameter types from each filter if it is present in the $_POST array. These are then imploded into the query, parameters are bound and the query executed.
if (isset($_POST['filtersubmit'])) {
$params = array();
$paramtypes = array();
$wheres = array();
if (isset($_POST['firstdate'], $_POST['lastdate'])) {
$date1 = date_create_from_format('m/d/Y', $_POST['firstdate']);
$date2 = date_create_from_format('m/d/Y', $_POST['lastdate']);
if (!empty($date1) && !empty($date2)) {
array_push($params, $date1->format('Y-m-d'), $date2->format('Y-m-d'));
array_push($paramtypes, 's', 's');
array_push($wheres, 'datum BETWEEN ? AND ?');
}
}
if (isset($_POST['projekt'])) {
$project = $_POST['projekt'];
if (is_numeric($project) && $project >= 0 && $project <= 2) {
array_push($params, $project);
array_push($paramtypes, 'i');
array_push($wheres, 'projekt = ?');
}
}
$sql = 'SELECT * FROM zapasy';
if (count($wheres)) {
$sql .= ' WHERE ' . implode(' AND ', $wheres);
}
$sql .= ' ORDER BY id DESC';
$stmt = $conn->prepare($sql) or die($conn->error);
if (count($wheres)) {
$stmt->bind_param(implode('', $paramtypes), ...$params);
}
$stmt->execute() or die($stmt->error);
// bind results
$stmt->bind_result(/* variables corresponding to each field in SELECT */);
while ($stmt->fetch()) {
// do something with the data
}
}