mysql> select id,name,mac from computers where id='2339';
+------+-------------+-------------------+
| id   | name        | mac               |
+------+-------------+-------------------+
| 2339 | Sun Ray #63 | 00:03:BA:0D:EB:A5 |
+------+-------------+-------------------+


mysql> select * from networking_ports where device_on='2339';
+------+-----------+-------------+------------------------+--------+-------------------+----------------+--------+
| ID   | device_on | device_type | iface                  | ifaddr | ifmac             | logical_number | name   |
+------+-----------+-------------+------------------------+--------+-------------------+----------------+--------+
| 1521 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0E:FD:C1 |              0 | Port 0 |
| 1522 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0E:F9:82 |              0 | Port 0 |
| 1523 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0E:FD:A7 |              0 | Port 0 |
| 1524 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:AD:F5 |              0 | Port 0 |
| 1525 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0F:00:15 |              0 | Port 0 |
| 1526 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0F:00:15 |              0 | Port 0 |
| 1527 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:CF:B4 |              0 | Port 0 |
+------+-----------+-------------+------------------------+--------+-------------------+----------------+--------+
7 rows in set (0.00 sec)

update networking_ports set ifmac=(select mac from computers where networking_ports.device_on=computers.id limit 1);

mysql> select * from networking_ports where device_on='2339';
+------+-----------+-------------+------------------------+--------+-------------------+----------------+--------+
| ID   | device_on | device_type | iface                  | ifaddr | ifmac             | logical_number | name   |
+------+-----------+-------------+------------------------+--------+-------------------+----------------+--------+
| 1521 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
| 1522 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
| 1523 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
| 1524 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
| 1525 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
| 1526 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
| 1527 |      2339 |           1 | 100Mbps Ethernet (UTP) | N/A    | 00:03:BA:0D:EB:A5 |              0 | Port 0 |
+------+-----------+-------------+------------------------+--------+-------------------+----------------+--------+

-- Started with this but I was testing order and limit which can't be used in mutiple table update
update networking_ports,computers set networking_ports.ifmac=computers.mac networking_ports.device_on=computers.id;

So 'Device_on' matches an ID in a table called computers.  I want to change all ifmac in networking_ports that match the first device_on to the computers.id