Changing Mysql functions to Mysqli breaks the script - php

Question

I have this script that deletes a certain picture from the website. It's written with mysql functions so i wanted to update it to mysqli but doing so makes the script stop working. No die message from the script are shown no php errors and adding error_reporting(E_ALL); doesn't show any errors either.
Original script:
if(isset($_POST['F3Verwijderen']))
try
{
//delete the file
$sql = "SELECT PandFoto3 FROM tblpand WHERE `PK_Pand` = '".$pandid."'";
$con = mysql_connect('WEBSITE.mysql', 'WEBSITE', 'PASS');
if (!$con) {
die('Could not connect: ' . mysql_error());
}
mysql_select_db("WEBSITE");
$result = mysql_query($sql, $con);
while ($row = mysql_fetch_array($result)) {
if(file_exists($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3'])) {
unlink($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3']);
} else {
echo $row['PandFoto3'];
}
}
//delete the path url from the database field
mysql_query("UPDATE tblpand SET PandFoto3 = NULL WHERE `PK_Pand` = '".$pandid."'");
mysql_close($con);
header('Location: ../admin/pand-aanpassen.php?id='.$pandid);
}
Updated to mysqli:
try
{
//delete the file
$sql = "SELECT PandFoto3 FROM tblpand WHERE `PK_Pand` = '".$pandid."'";
$con = mysqli_connect('WEBSITE.mysql', 'WEBSITE', 'PASS');
if (!$con) {
die('Could not connect: ' . mysqli_error());
}
mysqli_select_db("WEBSITE");
$result = mysqli_query($sql, $con);
while ($row = mysqli_fetch_array($result)) {
if(file_exists($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3'])) {
unlink($_SERVER['DOCUMENT_ROOT'].'/'.$row['PandFoto3']);
} else {
echo $row['PandFoto3'];
}
}
//delete the path url from the database field
mysqli_query("UPDATE tblpand SET PandFoto3 = NULL WHERE `PK_Pand` = '".$pandid."'");
mysqli_close($con);
header('Location: ../admin/pand-aanpassen.php?id='.$pandid);
}

Answer 1

Edit:
"no php errors and adding error_reporting(E_ALL); doesn't show any errors either."
That's because it isn't a PHP issue, it's a MySQL issue.
Those are two different animals altogether.
As I said in commments, you need to switch these variables ($sql, $con) around ($con, $sql).
Then this:
$con = mysqli_connect('WEBSITE.mysql', 'WEBSITE', 'PASS');
Just use the 4th parameter instead of mysqli_select_db("WEBSITE"); where you didn't pass the connection variable to.
$con = mysqli_connect('WEBSITE.mysql', 'WEBSITE', 'PASS', 'WEBSITE');
The syntax is:
host
username
password (if any)
database
You also could have done mysqli_select_db($con, "WEBSITE");
Sidenote: In mysql_ (see footnotes), the connection comes last, unlike in mysqli_ which comes first.
Do the same for your UPDATE and pass the connection parameter first.
mysqli_query($con, "UPDATE...
Sidenote: To verify that the update truly was successful, use affected_rows()
http://php.net/manual/en/mysqli.affected-rows.php.
Another thing, mysqli_error() requires a connection to it mysqli_error($con) and check for errors for your queries.
I.e.:
$result = mysqli_query($con, $sql) or die(mysqli_error($con));
References:
http://php.net/manual/en/mysqli.query.php
http://php.net/manual/en/mysqli.error.php
http://php.net/manual/en/mysqli.select-db.php
Sidenote:
You're using try() but no catch(). Either remove it, or consult the manual:
http://php.net/manual/en/language.exceptions.php
Example #4 pulled from the manual:
<?php
function inverse($x) {
if (!$x) {
throw new Exception('Division by zero.');
}
return 1/$x;
}
try {
echo inverse(5) . "\n";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
} finally {
echo "First finally.\n";
}
try {
echo inverse(0) . "\n";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
} finally {
echo "Second finally.\n";
}
// Continue execution
echo "Hello World\n";
?>
Final notes:
Your present code is open to SQL injection. Use prepared statements, or PDO with prepared statements, they're much safer.
Footnotes: (MySQL and MySQLi comparison)
In regards to mysql_query():
mixed mysql_query ( string $query [, resource $link_identifier = NULL ]
http://php.net/manual/en/function.mysql-query.php
For mysqli_query():
mixed mysqli_query ( mysqli $link , string $query [, int $resultmode = MYSQLI_STORE_RESULT ] )
http://php.net/manual/en/mysqli.query.php