Need help with if else

I could not get the sortby working. I don't know know what I did wrong. Can Someone look at my code and see what went wrong.

Here is my part of code.
<?php
include ('dbc.php');

if ($db) {

$field = $_GET['sortby' ];

$sql = "SELECT * FROM missionary";

if(isset ($field)){
if ($click==1){
$sql = $sql.' ORDER BY '.$field. ' ASC';
$click=0;
}
else{
$sql = $sql.' ORDER BY '.$field. ' DESC';
$click=1;
}

} 

$result = mysql_query( $sql) or die(mysql_error( ));

echo "<table width='100%' border='0' cellspacing= '0' cellpadding= '0'>
<tr>
<th class='width1' ><a href='viewtest2. php?sortby= sex'>Elder/ Sister</a> </th> 
<th class='width2' ><a href='viewtest2. php?sortby= first_name' >First Name</th>
<th class='width4' ><a href='viewtest2. php?sortby= last_name' >Last Name</th>
<th class='width5' ><a href='viewtest2. php?sortby= month_start' >Month (start)</th>
<th class='width6' ><a href='viewtest2. php?sortby= year_start' >Year (start)</th>
<th class='width7' ><a href='viewtest2. php?sortby= month_end' >Month (end)</th>
<th class='width8' ><a href='viewtest2. php?sortby= year_end' >Year (end)</th>
<th class='width9' >Action</ th>
</tr>";
while($row = mysql_fetch_ array($result) )

//while($row = mysql_fetch_ assoc($result) )
{

echo "<tr>";
echo "<td>" . $row['sex'] . "&nbsp;</td> ";
echo "<td>" . $row['first_ name'] . "&nbsp;</td> ";

if (!empty($row[ 'maiden_name' ])) {
echo "<td>" . $row['last_name' ] . "&nbsp&#40". $row['maiden_ name'] . "&#41 &nbsp;</td>" ; }
else 
{echo "<td>" . $row['last_name' ] . "&nbsp;</td> "; }

echo "<td>" . $row['month_ start'] . "&nbsp;</td> ";
echo "<td>" . $row['year_start' ] . "&nbsp;</td> ";
echo "<td>" . $row['month_ end'] . "&nbsp;</td> ";
echo "<td>" . $row['year_end' ] . "&nbsp;</td> ";

//echo "<td><a href=edit_update. php?id=" . $row['id'] . ">Edit/Update< /a></td>" ;

echo "<td><a href=view.php? id=" . $row['id'] . ">View history</a>< /td>";

echo "</tr>"; 
}
echo "</table>";
}
else {
echo "Database NOT Found ";
}

mysql_close( $link) ;
?>

</table>
</body>
</html>

 

It did not work. Here is my code

if(isset($_GET[ 'sortby'] == ""){
if ($orderby == 'DESC'{
$sql = $sql.' ORDER BY '.$field. ' DESC';
$orderby = 'ASC';
}
else{
$sql = $sql.' ORDER BY '.$field. ' ASC';
$orderby = 'DESC';
}
}