PHP5 codes that search MYSQL database

I have been using the codes below for searching mysql databases for quite sometime and it had benn working fine for me, but now (may be due to newer versions of php) they no longer work. Can someone please either correct them or send me new codes for the newer versions of php(php5).

I call this code, search.php, while the one after this is called view.php

The table is personnel with columns (id-auti_increment, firstname,lastname,nick,email,salary)

<HTML>
<?php
if ($searchstring)
{
$sql="SELECT * FROM personnel WHERE $searchtype LIKE '%$searchstring%' ORDER BY firstname ASC";
$db = mysql_connect("localhost", "root", "");
mysql_select_db("learndb",$db);
$result = mysql_query($sql,$db);
echo "<TABLE BORDER=2>";
echo"<TR><TD><B>Full Name</B><TD><B>Nick Name</B><TD><B>Options</B></TR>";
while ($myrow = mysql_fetch_array($result))
{
echo "<TR><TD>".$myrow["firstname"]."
".$myrow["nick"];
echo "<TD><a href=\"view.php?id=".$myrow[id]."\">View</a>";
}
echo "</TABLE>";
}
else
{
?>
<form method="POST" action="<?php $PHP_SELF?>">
<table border="2" cellspacing="2">
<tr><td>Insert you search string here</td>
<td>Search type</td></tr>
<tr>
<td><input type="text" name="searchstring" size="28"></td>
<td><select size="1" name="searchtype">
<option selected value="firstname">First Name</option>
<option value="lastname">Last Name</option>
<option value="nick">Nick Name</option>
<option value="email">Email</option>
</select></td>
</tr>
</table>
<p><input type="submit" value="Submit" name="B1"><input type="reset" value="Reset"
></p>
</form>
<?php
}
?>
</HTML>

This is view.php
<HTML>
<?php
$db = mysql_connect("localhost", "root", "");
mysql_select_db("learndb",$db);
$result = mysql_query("SELECT * FROM personnel WHERE id=$id",$db);
$myrow = mysql_fetch_array($result);
echo "First Name: ".$myrow["firstname"];
echo "<br>Last Name: ".$myrow["lastname"];
echo "<br>Nick Name: ".$myrow["nick"];
echo "<br>Email address: ".$myrow["email"];
echo "<br>Salary: ".$myrow["salary"];
?>
</HTML>

Please why is this code no more working and what is the solution.

Thanks.

okonjiaustin