how do I check for a text file is empty in php and if it is finished executing?

I have a code that runs a simple query like this

select * from tabela where coluna1 = 'valor';

Then I have a variable that brings a txt file

$filename = "C:/Programfile/arquivo.txt";

Then I make this condition below

if (file_exists($filename)) {
    rename($filename,$filename.".old");
}
$file = fopen($filename,"a+");

After this I do the while of the query

while ($row = mysql_fetch_array($sql))
{
            $content  = $row[0];
            $content .= "\r";
            $content .= "\n";   

            $result = fputs($file,$content);        

//break;
}
fclose($file);

The result of the query goes into the text file using vbs only I have a problem that when the query has no record the text file is empty and I am not getting to execute the script when the query does not return record can someone help me?

I already tried to do this and it did not work

if(filesize($filename)){
   exit;
}

or in the place of exit already put return false e die() and did not work.