export_excel.php

<?php
require_once 'vendor/autoload.php';
require_once 'config.php';

use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Writer\Xlsx;

$date = $_POST['date']; // Get the user-defined date from a form

// Fetch data from the "data_storage" table
$stmt = $conn->prepare("SELECT * FROM data_storage WHERE DATE(created_at) = :date");
$stmt->bindParam(':date', $date);
$stmt->execute();
$data = $stmt->fetchAll(PDO::FETCH_ASSOC);

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

// Write data to the spreadsheet
foreach ($data as $index => $row) {
    $sheet->fromArray(json_decode($row['register_data'], true), null, "A" . ($index + 1));
}

$writer = new Xlsx($spreadsheet);
$filename = "data_export_" . $date . ".xlsx";
$writer->save($filename);

header("Content-Type: application/vnd.ms-excel");
header("Content-Disposition: attachment; filename=\"$filename\"");
header("Cache-Control: max-age=0");
readfile($filename);
unlink($filename);
?>