PHP checking Serial Number (data) exists before submiting data - php

Question

I am trying to run a php upload which checks to see if a serial number already exists then if it doesnt submits data.
so :
Submit form --> PHP Checks DB for Duplicate Serial number --> If Serial number Does not Exist then post data // If Does Exist ignore input
However what ever i try doesnt seem to work. The following is my code but no matter what i do it submits the data even though the serial number already exists.
Form:
<form id="form1" action="senddata.php" name="form1" method="post">
<table class="table2" cellpadding="0" cellspacing="0">
<tr><td colspan="3"><input type="button" onClick="update()" value="Get Details"></td></tr>
<tr>
<td><label for="description">Description:</label></td>
<td><input tabindex="0" required type="text" name="description" id="description"></td>
</tr>
<tr>
<td><label for="nameofcomputer">Computer Code:</label></td>
<td><input tabindex="1" required type="text" name="nameofcomputer" id="nameofcomputer"></td>
</tr>
<tr>
<td><label for="make">Make:</label></td>
<td><input tabindex="2" required type="text" name="make" id="make"></td>
</tr>
<tr>
<td><label for="model">Model:</label></td>
<td><input tabindex="3" required type="text" name="model" id="model"></td>
</tr>
<tr>
<td><label for="serial">Serial Number:</label></td>
<td><input tabindex="4" required type="text" name="serial" id="serial"></td>
</tr>
<tr>
<td><label for="inputname">Your Name: </label></td>
<td><input tabindex="5" required id="inputname" name="inputname">
</td>
</tr>
</table>
<input required type="submit" name="submit" id="submit" value="Submit">
</form>
PHP
$desc=$_POST['description'];
$code=strtoupper($_POST['nameofcomputer']);
$make=$_POST['make'];
$model=$_POST['model'];
$serial=strtoupper($_POST['serial']);
$user=$_POST['inputname'];
$type='1';
$org='-1';
$control = "8670";
$now = new DateTime(null, new DateTimeZone('Europe/London'));
$date = $now->format('Y-m-d H:i:s');
$conn = sqlsrv_connect( $serverName, $connectionInfo);
$dupe = sqlsrv_query($conn, "SELECT * FROM Asset WHERE Serial_Number = '$serial'");
$num_rows = sqlsrv_num_rows($dupe);
if ($num_rows == 0) {
$tsql = "INSERT INTO Asset (Name, Asset_Type_ID, Ref_Code, Owner_Organisation_ID, Make, Model, Serial_Number, Current_Location, Start_Date)
VALUES ('$desc', '$type', '$code', '$org', '$make', '$model', '$serial', '$user', '$date')";
sqlsrv_query( $conn, $tsql);
echo "Asset Uploaded";
} else {
echo 'Error! Already on our database!';
}
Any help to get this working is appreciated.

Answer 1

I replaced
$dupe = sqlsrv_query($conn, "SELECT Serial_Number FROM Asset WHERE Serial_Number = '$serial'");
with
$dupe = sqlsrv_query($conn, "SELECT Serial_Number FROM Asset WHERE Serial_Number = '$serial'", array(), array("Scrollable"=>"buffered"));
and it worked perfectly.
Thanks to those who helped me figure out where the code was going wrong.