publicly populate a list field

Hello,

How can I publicly populate a cms builder multiple-select list field?

I have a list field called 'activity' that is grabbing it's values from another table 'activities' where $num is the value and $title is the label.

At the top of my page that has the html form, the mysql UPDATE statement for the activity field is as follows:

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activity = '".mysql_real_escape_string( $_REQUEST['activity'] )."',

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then in my html form

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<select multiple="multiple" name="activity" id="activity">
<?php foreach ($activitiesRecords as $recordActivity): ?>
<option value="<?php echo $recordActivity['num'] ?>"><?php echo $recordActivity['title'] ?></option><?php endforeach; ?>
</select>
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On the html form, a user can select multiple activities, but when the record is added to cms builder only the last selected activity becomes checked in the cms builder record.

Any ideas?

Thanks