<?php

    $mysqli = new mysqli("host", "username", "password", "database");
    $sql = "SELECT name FROM countries
            WHERE name LIKE '%".$_GET['query']."%'
            LIMIT 10";
    $result = $mysqli->query($sql);
    $data = [];
    while($row = $result->fetch_assoc()){
         $data[] = $row['name'];
    }
    echo json_encode($data);
?>