Duplicating result due to loop - php

Question

So my code get a value from previous page, compare it with a table field in the database and display success or failure. Here is the original code:
<?php
if ($_GET['q'] !='')
{
include('config.inc');
$foo = $_GET['q'];
$query= "INSERT INTO register(name) VALUES('$foo')";
$result = mysql_query("SELECT * FROM user_student");
while($row = mysql_fetch_array($result))
{
$id= $row['sid'];
if($id==$foo)
{
$res = mysql_query($query);
if ($res)
{
echo 'Insertion ok';
}
else
{
echo " ";
echo "Attendance already taken for $foo";
}
}
else
{
echo " ";
echo "Student $foo does not exist!!";
}
}
}
else echo "Invalid Command";
?>
Am having duplicating result e.g Student 1124 does not exist!! 10times. I've modify the code to:
while($row = mysql_fetch_array($result))
{
$id= $row['sid'];
if($id==$foo)
{
$res = mysql_query($query);
}
else
{
echo " ";
echo "Student $foo does not exist!!";
}
}
if ($res)
{
echo 'Insertion ok';
}
else
{
echo " ";
echo "Attendance already taken for $foo";
}
So i've placed the $res outside the loop to avoid duplication result but now it says: variable cannot be resolved Any suggestions?

Answer 1

A bit of changed version of CaldasGSM:
<?php
if (!empty($_GET['q']))
{
include('config.inc');
$foo = mysql_real_escape_string($_GET['q']);
$result = mysql_query("SELECT * FROM user_student WHERE sid = '{$foo}'");
$num_rows = mysql_num_rows($result);
if($num_rows > 0)
{
$res = mysql_query("INSERT INTO register(name) VALUES('$foo')");
if ($res)
{
echo 'Insertion ok';
}
else
{
echo " ";
echo "Attendance already taken for $foo";
}
}
else
{
echo " ";
echo "Student $foo does not exist!!";
}
}
else
{
echo "Invalid Command";
}
?>

Answer 2

maybe something like
<?php
if ($_GET['q'] !='')
{
include('config.inc');
$foo = $_GET['q'];
$result = mysql_query("SELECT * FROM user_student");
$bRecordExists = false;
while($row = mysql_fetch_array($result))
{
$id= $row['sid'];
if($id==$foo)
{
$bRecordExists = true;
break;
}
}
if($bRecordExists)
{
$res = mysql_query("INSERT INTO register(name) VALUES('$foo')");
if ($res)
{
echo 'Insertion ok';
}
else
{
echo " ";
echo "Attendance already taken for $foo";
}
}
else
{
echo " ";
echo "Student $foo does not exist!!";
}
}
else
{
echo "Invalid Command";
}
?>