I am using RSFormsPro in my Joomla site to create forms
I have 2 x Selectize fields
Field 1 - inventory_deck, in the Items field I have below code to get the list from the database:
//<code>

$items = array();

$db = JFactory::getDbo();

$items[] = "|Please Select[c]";

$db->setQuery("SELECT FieldValue, FieldValue FROM `inv_rsform_submission_values` WHERE `FieldName` = 'deck'");
$results = $db->loadObjectList();

foreach ($results as $result) {
$value = $result->FieldValue;
$label = $result->FieldValue;
$items[] = $value.'|'.$label;
}

$items = implode("\n", $items);

return $items;
//</code>

This works and the list is populated with the content I need

Field 2 - inventory_location_1, in the Items field I have below code to get the list from the database but I need this list to only be populated after I select a value for Field 1:
The v1.FieldValue = '7. Tank Deck' needs to be dynamically updated by the selection made in Field 1

//<code>

$items = array();

$db = JFactory::getDbo();

$items[] = "";


$db->setQuery("SELECT v2.FieldValue as location
FROM inv_rsform_submission_values v1
JOIN inv_rsform_submission_values v2 ON v1.SubmissionId = v2.SubmissionId
WHERE v1.FieldName = 'location_deck' AND v1.FieldValue = 'THIS NEEDS TO BE THE VALUE FROM FIELD 1' AND v2.FieldName = 'location'");
$results = $db->loadObjectList();

foreach ($results as $result) {
$value = $result->location;
$label = $result->location;
$items[] = $value.'|'.$label;
}

$items = implode("\n", $items);

return $items;
//</code>