CREATE PROCEDURE vpn_assign_nodes(IN node __NODENAME_T__, IN node_count INT)
BEGIN
    DROP TABLE IF EXISTS vpn_assign_tmp;
    CREATE TEMPORARY TABLE vpn_assign_tmp
        SELECT p.vpn_id, p.vpn_type, p.vpn_data, c.cred_id, c.credentials
        FROM vpn_pool p JOIN vpn_cred_pool c USING (vpn_type)
        WHERE 0;

    SET @nodes_needed = node_count;
    SET @done = 0;
    SET @my_vpn_id = NULL;
    SET @my_cred_id = NULL;

    WHILE (@nodes_needed > 0 AND @done != 1) DO

        START TRANSACTION;

        SET @my_vpn_id = NULL;

        SELECT
            vpn_pool.vpn_id, vpn_pool.vpn_type, vpn_pool.vpn_data,
            cpool.credentials, cpool.cred_id
        FROM vpn_pool
        JOIN vpn_provider_common AS prov
            ON vpn_pool.vpn_type = prov.vpn_type
        JOIN vpn_cred_pool cpool
            ON (cpool.vpn_type = vpn_pool.vpn_type AND
            -- Only select those credentials which haven't been exhausted in full yet
                (cpool.cred_busy < prov.semaphore_needed
                OR prov.semaphore_needed = 0)
            )
        WHERE
            vpn_pool.vpn_node IS NULL

        -- No need for randomization, is there?
        ORDER BY RAND()
        LIMIT 1
        INTO @my_vpn_id, @my_vpn_type, @my_vpn_data, @my_credentials, @my_cred_id
        FOR UPDATE;

        IF (@my_vpn_id IS NULL) THEN
            SET @done = 1;
            COMMIT;
        ELSE
            INSERT INTO vpn_assign_tmp (vpn_id, vpn_type, vpn_data,
                cred_id, credentials)
                VALUES(@my_vpn_id, @my_vpn_type, @my_vpn_data, @my_cred_id,
                    @my_credentials);

            UPDATE vpn_pool
                JOIN vpn_provider_common prov
                    ON vpn_pool.vpn_type = prov.vpn_type
                LEFT OUTER JOIN vpn_cred_pool cpool
                    ON cpool.cred_id = @my_cred_id
                SET vpn_pool.vpn_node = node,
                    vpn_pool.vpn_conn_id = CONNECTION_ID(),
                    vpn_pool.last_updated = UNIX_TIMESTAMP(NOW()),
                    vpn_pool.cred_id = @my_cred_id,
                    cpool.cred_busy = cpool.cred_busy + 1
                WHERE vpn_id = @my_vpn_id;

            SET @nodes_needed = @nodes_needed - 1;
        END IF;
        COMMIT;
    END WHILE;
    SELECT vpn_id, vpn_type, vpn_data, credentials FROM vpn_assign_tmp;
END $$

+---------+------+-----------------------------------------------------+
| Level   | Code | Message                                             |
+---------+------+-----------------------------------------------------+
| Warning | 1329 | No data - zero rows fetched, selected, or processed |
+---------+------+-----------------------------------------------------+
1 row in set (0.00 sec)