查询不返回任何记录，但phpmyadmin返回

我在查询数据库的结果时遇到了麻烦。当我在phpmyadmin中输入查询时，它工作得很好。但是在php中执行完全相同的查询不会返回任何结果。

我已经在网上搜索了很长一段时间了，但我到处都发现这类问题被评为最佳答案。也许我遗漏了什么，你们可以帮我。

查询:

SELECT current_consumption, current_delivery, UNIX_TIMESTAMP(timestamp) FROM energydata WHERE timestamp > DATE_SUB(NOW(), INTERVAL 1 HOUR);

<?php
include "database.php";
$limit = (int)$_GET["limit"];
// Create connection
$conn = new mysqli($servername, $databaseUser, $databasePassword, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 
$sql = "SELECT current_consumption, current_delivery, UNIX_TIMESTAMP(timestamp) FROM energydata WHERE timestamp > DATE_SUB(NOW(), INTERVAL 1 HOUR)";
$result = $conn->query($sql);
$json = array();
if ($result->num_rows > 0) {
    $columns = array(
        array(
            'id' => 'date',
            'label' => 'Date',
            'type' => 'datetime'),
        array(
            'id' => 'consumption',
            'label' => 'Consumption',
            'type' => 'number'),
        array(
            'id' => 'delivery',
            'label' => 'Delivery',
            'type' => 'number')
        );
    $rows = array();
    // output data of each row
    while($row = $result->fetch_assoc()) {
        $date = array();
        $date = date_parse($row['timestamp']);
        $currentRow = array(
            'c' => array(
                array(
                    'v' => 'Date('. $row['UNIX_TIMESTAMP(timestamp)'] .'000)'
                ),
                array(
                    'v' => $row['current_consumption']
                ),
                array(
                    'v' => $row['current_delivery']
                )
            )
        );
        array_push($rows, $currentRow);
    }
    $json = array(
        'cols' => $columns,
        'rows' => $rows);
}
echo json_encode($json);