Is it possible to have a HTML SELECT/OPTION value

问题:

The following is a snippet from my HTML form which pulls the options from the table rows accordingly.

What I want to do is have the first option value to be NULL so when no choice is made, NULL is entered when the form is submitted to the database.

    <td>Type</td>
    <td>:</td>
    <td><select name="type_id" id="type_id" class="form">
    <option value=""></option>
        <?php 
            $sql = mysql_query("SELECT type_id, type FROM $tbl_add_type") or die(mysql_error());
            while ($row = mysql_fetch_array($sql))
                {
                    echo "<option value=".$row['type_id'].">" . $row['type'] . "</option>";
                }
        ?>
    </select>*</td>

Is this possible? Or could someone suggest an easier/better way of doing this?

Thanks

Update: Thanks for the answer, I'm using the method detailed below to convert it to NULL.

if ($_POST['location_id'] === '')
                    {
                        $_POST['location_id'] = 'NULL';
                    }

However when trying to use this NULL value with the following query it does not work.

UPDATE addresses SET location_id='NULL' WHERE ipid = '4791'

I know it needs to be location_id=NULL instead but don't know how to do this...

Update 2: this is how my queries work:

if ($_POST['location_id'] === '')
{
$_POST['location_id'] = 'NULL'; // or 'NULL' for SQL
}

$notes=isset($_POST['notes']) ? mysql_real_escape_string($_POST['notes']) : '';
//$location_id=isset($_POST['location_id']) ? mysql_real_escape_string($_POST['location_id']) : '';
$ipid=isset($_POST['ipid']) ? mysql_real_escape_string($_POST['ipid']) : '';


$sql="UPDATE addresses 
    SET notes='$notes', location_id='$location_id'
    WHERE ipid = '$ipid'";


mysql_query($sql) or die(mysql_error());

回答1:

No, POST/GET values are never null. The best they can be is an empty string, which you can convert to null/'NULL'.

if ($_POST['value'] === '') {
    $_POST['value'] = null; // or 'NULL' for SQL
}

回答2:

All you need is a check on the post side of things.

if(empty($_REQUEST['type_id']) && $_REQUEST['type_id'] != 0)
    $_REQUEST['type_id'] = null;

回答3:

Yes, it is possible. You have to do something like this:

if(isset($_POST['submit']))
{
  $type_id = ($_POST['type_id'] == '' ? "null" : "'".$_POST['type_id']."'");
  $sql = "INSERT INTO `table` (`type_id`) VALUES (".$type_id.")";
}

It checks if the $_POST['type_id'] variable has an empty value. If yes, it assign NULL as a string to it. If not, it assign the value with ' to it for the SQL notation

回答4:

In php 7 you can do:

$_POST['value'] ?? null;

If value is equal to '' as said in other answers it will also send you null.

回答5:

that's why Idon't like NULL values in the database at all.
I hope you are having it for a reason.

if ($_POST['location_id'] === '') {
  $location_id = 'NULL';
} else {
  $location_id = "'".$_POST['location_id']."'";
}
$notes = mysql_real_escape_string($_POST['notes']);
$ipid  = mysql_real_escape_string($_POST['ipid']);

$sql="UPDATE addresses 
    SET notes='$notes', location_id=$location_id
    WHERE ipid = '$ipid'";

echo $sql; //to see different queries this code produces
// and difference between NULL and 'NULL' in the query