Only update when value is not null mySQL - php

Question

I am working on an update query where the values should only update when the value is not null or empty. Now it updates everything regardless the value. Please help me out with this one.
$query = "UPDATE bundels
SET batchkosten = CASE WHEN ". $_POST['batchkosten'] . " IS NOT NULL
THEN ". $_POST['batchkosten'] . "
ELSE batchkosten
END CASE,
CASE WHEN ". $_POST['maandelijkse_kosten'] . " IS NOT NULL
THEN ". $_POST['maandelijkse_kosten'] . "
ELSE maandelijkse_kosten
END CASE,
CASE WHEN ". $_POST['aanmeldkosten'] . " IS NOT NULL
THEN ". $_POST['aanmeldkosten'] . "
ELSE aanmeldkosten
END CASE,
CASE WHEN ". $_POST['transactiekosten'] . " IS NOT NULL
THEN ". $_POST['transactiekosten'] . "
ELSE transactiekosten
END CASE,
CASE WHEN ". $_POST['referral'] . " IS NOT NULL
THEN ". $_POST['referral'] . "
ELSE referral
END CASE,
CASE WHEN ". $_POST['actief'] . " IS NOT NULL
THEN ". $_POST['actief'] . "
ELSE actief
END CASE
WHERE bundel_id = ". $_POST['bundel_id'] . "";
$result = mysql_query($query, $db) or die ('FOUT: werkt niet');
header ("Location: vergelijker_bewerken.php");
} else {
$bundels = mysql_query("SELECT bundels.psp_id, psp.psp_id, psp_naam, bundels.bundel_id, batchkosten, maandelijkse_kosten, aanmeldkosten, transactiekosten, referral, actief from bundels
JOIN psp
ON psp.psp_id = bundels.psp_ID");
}

Answer 1

Use Prepared Statements to escape user input and avoid SQL syntax errors and SQL injections.
You can use a case
UPDATE bundels
SET batchkosten = case when ? is not null and length(?) > 0
then ?
else batchkosten
end,
...
Your current query translates to (which should throw an error actually)
UPDATE bundels
SET batchkosten = CASE WHEN ? length(?) > 0
THEN ?
ELSE batchkosten
END
WHERE bundel_id = ?
But use instead:
SET batchkosten = CASE WHEN ? is not null and length(?) > 0

Answer 2

you can write script some like this maybe:
$query = "Update bundels SET ";
$columns = array( "batchkosten",
"maandelijkse_kosten",
"aanmeldkosten",
"transactiekosten",
"referral",
"actief");
foreach($columns as $column){
if(isset($_POST[$column]) && !empty($_POST[$column])){
$query .= $column . " = " $_POST[$column] . " ";
}
}
$query .= " WHERE bundel_id = " . $_POST['bundel_id'];

Answer 3

Change the query to this
$query= "UPDATE bundels SET
batchkosten = ' ". $_POST['batchkosten'] . " ',
maandelijkse_kosten = ' ". $_POST['maandelijkse_kosten'] . " ',
aanmeldkosten = ' ". $_POST['aanmeldkosten'] . " ',
transactiekosten = ' ". $_POST['transactiekosten'] . " ',
referral = ' ". $_POST['referral'] . " ',
actief = ' ". $_POST['actief'] . " '
WHERE bundel_id = ". $_POST['bundel_id'] . " ".
"and your_attribut is not null and your_attribut != ''";
Don't forget to change "your_attribut".