how to update one or more fields ignoring the empty fields into mysql database?

Question

i am seeking help on ignoring null values for updating the mysql database:-

$cst = $_POST['custname'];
$a = $_POST['tel'];
$b = $_POST['fax'];
$c = $_POST['email'];
$sql = mysql_query("UPDATE contacts SET TEL = '$a', FAX = '$b', EMAIL = '$c'
                    WHERE Cust_Name = '$cst' ");

how do i incorporate an option where the user can only select one or all fields for updation.

i tried using the following code based on responses received but it does the same thing. overwrites the existing data with the blank ones.

$upd = mysql_query("UPDATE custcomm_T SET 
Telephone = ".(is_null($a)?'Telephone':"'$a'").",
Fax = ".(is_null($b)?'Fax':"'$b'").",
Mobile = ".(is_null($c)?'Mobile':"'$c'").",
EMail = ".(is_null($d)?'EMail':"'$d'").",
trlicense = ".(is_null($e)?'trlicense':"'$e'").",
trlicexp = ".(is_null($f)?'trlicexp':"'$f'")."
WHERE Cust_Name_VC = '$g' ") or die(mysql_error());

Answer 1

Firstly remember to escape any strings coming to you via POST, GET, or REQUEST (read up on SQL injection attacks if you're unsure why).

Something like this might work:

$semaphore = false;
$query = "UPDATE contacts SET ";
$fields = array('tel','fax','email');
foreach ($fields as $field) {
   if (isset($_POST[$field]) and !empty($_POST[$field]) {
     $var = mysql_real_escape_string($_POST[$field]);
     $query .= uppercase($field) . " = '$var'";
     $semaphore = true;
   }
}

if ($semaphore) {
   $query .= " WHERE Cust_Name = '$cst'";
   mysql_query($query);
}

NB : Do not ever simply loop through your $_POST array to create a SQL statement. An opponent can add extra POST fields and possibly cause mischief. Looping through a user input array can also lead to an injection vector: the field names need to be added to the statement, meaning they're a potential vector. Standard injection prevention techniques (prepared statement parameters, driver-provided quoting functions) won't work for identifiers. Instead, use a whitelist of fields to set, and loop over the whitelist or pass the input array through the whitelist.

Answer 2

You need to build your query. Something like this:

$query = 'update contacts set ';
if ($_POST['tel'] != '') $query .= 'TEL="'.$_POST['tel'].'", ';
if ($_POST['fax'] != '') $query .= 'FAX="'.$_POST['fax'].'", ';
if ($_POST['email'] != '') $query .= 'EMAIL="'.$_POST['email'].'", ';
$query .= "Cust_Name = '$cst' where Cust_Name = '$cst'";

The last update field: Cust_Name = '$cst' basically is to 'remove' the last comma.

Answer 3

Keeping in mind that $_POST values should be cleaned before use, and that all $_POST values are strings, so an empty field is '' and not null, something like this will work:

        foreach ($_POST as $var=>$value) {
            if(empty($value)) continue; //skip blank fields (may be problematic if you're trying to update a field to be empty)
            $sets[]="$var= '$value";

        }
        $set=implode(', ',$sets);
        $q_save="UPDATE mytable SET $set WHERE blah=$foo";

Answer 4

This should work (the MySQL way):

"UPDATE `custcomm_T`
SET `Telephone` = IF(TRIM('" . mysql_real_escape_string($a) . "') != '', '" . mysql_real_escape_string($a) . "', `Telephone`),
SET `Fax` = IF(TRIM('" . mysql_real_escape_string($b) . "') != '', '" . mysql_real_escape_string($b) . "', `Fax`),
SET `Mobile` = IF(TRIM('" . mysql_real_escape_string($c) . "') != '', '" . mysql_real_escape_string($c) . "', `Mobile`),
SET `EMail` = IF(TRIM('" . mysql_real_escape_string($d) . "') != '', '" . mysql_real_escape_string($d) . "', `EMail`),
SET `trlicense` = IF(TRIM('" . mysql_real_escape_string($e) . "') != '', '" . mysql_real_escape_string($e) . "', `trilicense`),
SET `trlicexp` = IF(TRIM('" . mysql_real_escape_string($f) . "') != '', '" . mysql_real_escape_string($f) . "', `trlicexp`)
WHERE Cust_Name_VC = '" . mysql_real_escape_string($g) . '";

I've tried to keep the columns and variables to what you have posted in your question, but feel free to correct as per your schema.

Hope it helps.

Answer 5

Loop over the optional input fields, building up which fields to set. The field names and values should be kept separate so you can use a prepared statement. You can also loop over required fields as a basic validation step.

# arrays of input => db field names. If both are the same, no index is required.
$optional = array('tel' => 'telephone', 'fax', 'email');
$required = array('custname' => 'cust_name');

# $input is used rather than $_POST directly, so the code can easily be adapted to 
# work with any array.

$input =& $_POST;

/* Basic validation: check that required fields are non-empty. More than is 
 necessary for the example problem, but this will work more generally for an 
 arbitrary number of required fields. In production code, validation should be 
 handled by a separate method/class/module.
 */
foreach ($required as $key => $field) {
    # allows for input name to be different from column name, or not
    if (is_int($key)) {
        $key = $field;
    }
    if (empty($input[$key])) {
        # error: input field is required
        $errors[$key] = "empty";
    }
}
if ($errors) {
    # present errors to user.
    ...
} else {
    # Build the statement and argument array.
    $toSet = array();
    $args = array();
    foreach ($optional as $key => $field) {
        # allows for input name to be different from column name, or not
        if (is_int($key)) {
            $key = $field;
        }
        if (! empty($input[$key])) {
            $toSet[] = "$key = ?";
            $args[] = $input[$key];
        }
    }
    if ($toSet) {
        $updateContactsStmt = "UPDATE contacts SET " . join(', ', $toSet) . " WHERE cust_name = ?";
        $args[] = $input['custname'];
        try {
            $updateContacts = $db->prepare($updateContactsStmt);
            if (! $updateContacts->execute($args)) {
                # update failed
                ...
            }
        } catch (PDOException $exc) {
            # DB error. Don't reveal exact error message to non-admins.
            ...
        }
    } else {
        # error: no fields to update. Inform user.
        ...
    }
}

This should be handled in a data access layer designed to map between the database and program objects. If you're clever, you can write a single method that will work for arbitrary models (related forms, tables and classes).

Answer 6

mysql_query("
    UPDATE contacts 
    SET 
        TEL = ".(is_null($a)?'TEL':"'$a'").", 
        FAX = ".(is_null($b)?'FAX':"'$b'").", 
        EMAIL = ".(is_null($c)?'EMAIL':"'$c'")."
    WHERE Cust_Name = '$cst'
");