<?php
$host = '127.0.0.1';
$db   = 'dbname';
$user = 'root';
$pass = '123456';
$charset = 'utf8mb4';

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$opt = [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
    PDO::ATTR_EMULATE_PREPARES   => false,
];
$pdo = new PDO($dsn, $user, $pass, $opt);
$stmt = $pdo->prepare("SELECT * FROM `table`");
$stmt->execute();
header("Content-Type: text/csv");
header("Content-Disposition: attachment; filename=export_view".date('y-m-d').".csv");
$output = fopen("php://output", "w");
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    fputcsv($output, $row);
}
fclose($output);