<?php
$row_values = [
    'POS RETAIL|INVENTORY STANDARD',
    'POS RETAIL',
    'POS RETAIL|',
    'INVENTORY STANDARD'
];
 
$items = [];
 
//get all items from database and explode the concat values.
foreach ($row_values as $row) {
    $items = array_merge($items, explode('|', $row));
}
 
//get only the distinct items.
$items = array_unique($items);
 
//remove the emtpy items.
$items = array_filter($items);
 
//initialize the list.
$list = '<option value="">SELECT SOFTWARE / HARDWARE</option>';
 
//create the list of unique items.
foreach ($items as $item) {
    $list .= "<option value='$item'>$item</option>";
}
 
var_dump($list);

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