Untitled

<?php

session_start();

$jsonDates;
retrieve_trips($jsonDates);

function retrieve_trips(&$jsonDates)
{


    $sql = "SELECT * FROM events order by date";

    $conn = mysqli_connect('localhost', 'root', '', 'event');
    $query = mysqli_query($conn, $sql);
    $result = array();
    while ($row = mysqli_fetch_assoc($query)) {
    $data[] = $row;
    group_by("date",$row,$result);
}

// echo "<pre>" . var_export(array_keys($result), true) . "</pre>";
    // echo '<pre>'; print_r($data); echo '</pre>';
     $jsonDates=json_encode(array_keys($result));
    // echo $jsonDates;
	// return $trips;
}


function group_by($key, $val,&$result) {
        if(array_key_exists($key, $val)){
            $result[$val[$key]][] = $val;
        }else{
            $result[""][] = $val;

         }
}
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script src="sortable.js"></script>
    <link rel="stylesheet" href="index.css">
    <script src="index.js"></script>
    <title>Document</title>
</head>
<body>
    <div class="tab" data-dates=<?php echo $jsonDates; ?>>


    </div>


    <div id="container">

    </div>


</body>
</html>