src/Helper/PrepareCounter.php
public function prepare($value)
    {
        /** @var Importer $importer */
        $importer = $this->getVariably()->get('importer');
        $table = $importer->getCurrentTable();

        if (!isset($this->counter[$table])) {
            $db = $importer->getDb();
            $counter = $db->fetchOne('SELECT MAX(DISTINCT counter) AS counter FROM ' . $table);

            $this->counter[$table] = $counter['counter'] + 1;
        }

        return $this->counter[$table];
    }
public function prepare($value)
    {
        /** @var Importer $importer */
        $importer = $this->getVariably()->get('importer');
        $table = $importer->getCurrentTable();

        if (!isset($this->counter[$table])) {
            $db = $importer->getDb();
            $counter = $db->fetchOne('SELECT MAX(DISTINCT counter) AS counter FROM ' . $table);

            $this->counter[$table] = $counter['counter'] + 1;
        }

        return $this->counter[$table];
    }
This method check existing counter and if it isn`t exist it calculate a new one.

@param $value
@return mixed