public function setWhere()
    {
        // checking of Exact flag
        $index = 0;
        foreach ($this->data['where'] as $alias => $fields) {

            foreach ($fields as $field => $type) {
                // call expression handler
                $this->expressionRun($alias, $field, $type, $index);
                ++$index;
            }
        }

        return null;
    }