Exec命令在sql server中不起作用

Question

I am working on database migration. I have written a code for executing the command that retrieves the data from database and pushes into a csv file. This Works fine in MySQL but when I try to do the same in SQL Server it does not work. Infact when I copy paste the same command into command prompt it works fine. I double checked everything. I do not understand why its not working. It returns blank output. I have already tried many of the solutions provided before. None works. Any help on this is most appreciated.

Here is the code I am using:

//$sqlsrv is used to determine the database server type
  $str_query = voc_get_query_string($query);
  $output_uri = 'temporary://' . user_password();
  $file_path = drupal_realpath($output_uri . '.csv');
  if($sqlsrv){
    $exec_path = drupal_realpath('private://Binn\sqlcmd');
  }else{
    $exec_path = drupal_realpath('private://mysql');
  }
  $sql_uri = 'temporary://' . user_password();
  $sql_path = drupal_realpath($sql_uri);  
  $fp = fopen($sql_path, 'w');
  fputs($fp, $str_query);
  fclose($fp);
  global $databases;
  if ($sqlsrv) {
    $cmd = ($exec_path .
        ' -S ' . $databases['default']['default']['host'] .
        ' -d ' . $databases['default']['default']['database'] .
        ' -U ' . $databases['default']['default']['username'] .
        ' -P ' . $databases['default']['default']['password'] .
        ' -i ' . $sql_path . '>>'. $file_path .
        ' -s '. '"," -W -m10 -r1');
  }
  else {
    $cmd = ($exec_path . ' ' . $databases['default']['default'] 
        ['database'] .
        ' -h ' . $databases['default']['default']['host'] .
        ' -u ' . $databases['default']['default']['username'] .
        ' -p ' . $databases['default']['default']['password'] . ' < ' 
        . $sql_path .
        ' > ' . $file_path);
  }

  exec($cmd);
  watchdog('cmd', var_export($cmd, TRUE));