$mysqli = mysqli_connect('localhost', 'root', '123456', 'test');
$sql = 'select * from country';
$res = mysqli_query($mysqli, $sql);
header("Content-type:application/vnd.ms-excel");
header("Content-Disposition:filename=country.xls");
echo "code\t";
echo "name\t";
echo "population\t\n";
if(mysqli_num_rows($res) > 0) {
  while($row = mysqli_fetch_array($res)) {
    echo $row['code']."\t";
    echo $row['name']."\t";
    echo $row['population']."\t\n";
  }
}

$mysqli = mysqli_connect('localhost', 'root', '123456', 'test');
$sql = 'select * from country';
$res = mysqli_query($mysqli, $sql);
$file = fopen('./country.xls', 'w');
fwrite($file, "code\tname\tpopulation\t\n");
if(mysqli_num_rows($res) > 0) {
  while($row = mysqli_fetch_array($res)) {
    fwrite($file, $row['code']."\t".$row['name']."\t".$row['population']."\t\n");//这里写得不好，应该把所有文件内容组装到一个字符串中然后一次性写入文件。
  }
}
fclose($file);
echo 'http://www.jtw.com/....../country.xls';//这里返回文件路径给js

$path = './country.xls';
$file = fopen($path, 'r');
//标题行读取（第一行）
$row = fgets($file);
$row = explode("\t", $row);
$title = array();
foreach($row as $k => $v) {
  $title[$k] = str_replace("\n", '', $v);
}
//内容读取
$data = array();
$count = 0;
while(!feof($file)) {
  $row = fgets($file);
  $row = explode("\t", $row);
  if(!$row[0]) continue;//去除最后一行
  foreach($title as $k => $v) {
    $data[$count][$title[$k]] = $row[$k];
  }
  $count ++;
}
fclose($file);
echo '<pre>';
print_r($data);