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Asked: 2026-05-16T10:53:04+00:00

I’m relatively confused about this… I’ve got a table like: +—————-+————————————————–+——+—–+——————-+—————————–+ | Field |

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I’m relatively confused about this…

I’ve got a table like:


+----------------+--------------------------------------------------+------+-----+-------------------+-----------------------------+
| Field          | Type                                             | Null | Key | Default           | Extra                       |
+----------------+--------------------------------------------------+------+-----+-------------------+-----------------------------+
| dhcp           | int(10) unsigned                                 | NO   | PRI | 0                 |                             |
| ip             | int(10) unsigned                                 | NO   | PRI | 0                 |                             |
| mac            | varchar(17)                                      | YES  | MUL | NULL              |                             |
| lease          | enum('fr','a','fi','a','u') | NO   | MUL | free) |                                |                             |
| date           | timestamp                                        | NO   | MUL | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| uid            | varchar(255)                                     | YES  |     | NULL              |                             |
| starts_date    | datetime                                         | YES  |     | NULL              |                             |
| starts_weekday | tinyint(1)                                       | YES  |     | NULL              |                             |
| ends_date      | datetime                                         | YES  |     | NULL              |                             |
| ends_weekday   | tinyint(1)                                       | YES  |     | NULL              |                             |
| first_seen     | datetime                                         | YES  |     | NULL              |                             |
+----------------+--------------------------------------------------+------+-----+-------------------+-----------------------------+

I just added the first_seen column. The idea is that I will use INSERT… ON DUPLICATE KEY UPDATE. dhcp and ip are rightly primary keys, as I want to only have one record for them at a time. So if mac changes, it should update the existing row if one exists for that dhcp, ip combination.

however, I want to have first_seen updated every time a (ip, dhcp, mac) combination is seen… i.e. if the value of ‘mac’ changes, I want to update first_seen. If the value of ‘mac’ stays the same, I want to leave first_seen the same.

Is there any simple way to do this in SQL… i.e. an IF() or something? or do I have to handle this with another SELECT in the PHP script (keeping in mind that we’re parsing a file to get this data, and inserting abut 10-16k rows, so time is a factor).

Thanks,
Jason

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1 Answer

  1. Editorial Team

    Thanks for all the suggestions, guys. It turns out that I don’t need a trigger for this, just an IF at the beginning of the update statement.

    in the INSERT INTO… I have first_seen=CURRENT_TIMESTAMP

    Then at the beginning of the UPDATE I have

    first_seen = IF( mac != VAULES(MAC), CURRENT_TIMESTAMP, first_seen)

    This only updates first_seen if the mac changes, else it sets first_seen to itself (its current value).

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