MatthiasMullie\Scrapbook\Adapters\SQL::doIncrement PHP Method

    protected function doIncrement($key, $offset, $initial, $expire)
    {
        /*
         * I used to have all this logic in a huge & ugly query, but getting
         * that right on multiple SQL engines proved challenging (SQLite doesn't
         * do INSERT ... ON DUPLICATE KEY UPDATE ..., for example)
         * I'll just stuff it in a transaction & leverage existing methods.
         */
        $this->client->beginTransaction();
        $this->clearExpired();
        $value = $this->get($key);
        if ($value === false) {
            $return = $this->add($key, $initial, $expire);
            if ($return) {
                $this->client->commit();
                return $initial;
            }
        } elseif (is_numeric($value)) {
            $value += $offset;
            // < 0 is never possible
            $value = max(0, $value);
            $return = $this->replace($key, $value, $expire);
            if ($return) {
                $this->client->commit();
                return (int) $value;
            }
        }
        $this->client->rollBack();
        return false;
    }