How to exit if query does not return records?

Hi all . I wonder how i check if the bold query is returning no record and if no record returned the script display the following massage and the rest of script does not execute at all. I be happy if an expert show me how.Thanks

Code:

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You have no PlayLists. You Must create at least one PlayList to add songs to it, Please click here to Create a PlayList

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Code:

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......
$query2 = "select * from playlists where user_id='$username'"; //using user ID to get his playlist names
$result2 = mysql_query($query2) or die("Error with MySQL Statement! ".mysql_error()."<br>\nThe query was ".$query2);

//this line for dropdownbox
$option = "";


while($row2 = mysql_fetch_assoc($result2))
{

//This 2 line for drop downbox
extract ($row2);
    $option .= "<option value=\"$playlistname\">$playlistname</option>\r\n";

}   



?>
..... html and some php code later
......

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PHP Code:

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$query2 = "select * from playlists where user_id='$username'";  //using user ID to get his playlist names
$result2 = mysql_query($query2) or die("Error with MySQL Statement! ".mysql_error()."<br>\nThe query was ".$query2);

//this line for dropdownbox
$option = "";

if(mysql_num_rows($result2) == 0){
echo 'errormsg';
}
else{
while($row2 = mysql_fetch_assoc($result2))
{

//This 2 line for drop downbox
extract ($row2);
    $option .= "<option value=\"$playlistname\">$playlistname</option>\r\n";

} 
} 


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sumtin like that.