为连接查询执行mysql_list_fields

I am looking to populate an array of all columns that are being viewed in a query lets say

    $sql='SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
    FROM tutorials_tbl a, tcount_tbl b
    WHERE a.tutorial_author = b.tutorial_author';


    function getColoumns($sql) {
         $result = mysql_query("SHOW COLUMNS FROM (". $sql."));
  if (!$result) {
    echo 'Could not run query: ' . mysql_error();
  }
  $fieldnames=array();
  if (mysql_num_rows($result) > 0) {
    while ($row = mysql_fetch_assoc($result)) {
      $fieldnames[] = $row['Field'];
    }
  }

  return $fieldnames;
    }

I cant seem to get it right. Anyone out there who can help me out. Thanks in Advance.

SHOW COLUMNS does not allow for a subselect statement according to the MySQL documentation.

You could instead go for a combination of the original query, mysql_num_fields() and mysql_field_name():

function getColoumns($sql) {
  $result = mysql_query( $sql );
  if (!$result) {
    echo 'Could not run query: ' . mysql_error();
    // return from function here. don't know what value you need.
    return array()
  }

  $fieldnames = array();
  $fieldCount = mysql_num_fields($result);
  for( $i=0; $i<$fieldCount; $i++ ) {
    $fieldnames[] = mysql_field_name( $result , $i );
  }

  return $fieldnames;
}

^{Besides, take a look at Why shouldn't I use mysql_* functions in PHP? and/or make sure the query is not malicious!}