<?php
echo "<form action=\"\" method=\"post\">";
echo "<input type=\"text\" autocomplete=\"off\" name=\"feldname\" value=\"\" list=\"listenname\">";
echo "<input type=\"submit\">";
echo "</form>";

echo "<datalist id=\"listenname\">";

$sql = "SELECT 1, 2, 3, 4 FROM tabellenname";
foreach ($pdo->query($sql) as $row)
{
echo "<option label={$row['1']}, {$row['2']}, {$row['3']}>".$row['4']."</option>";
}

echo "</datalist>";
?>