No, it's the furthest from a home SC. If two are equally distant from a home SC, it's alphabetical.

Once I was attacking a CD country.
It had armies in Brest, Paris and Piedmont.

It lost a supply centre and disbanded Brest!

After that it lost another centre. It disbanded....Paris!

I thought, Brest is 0 spaces from a home SC, so is Paris. Piedmont is 1 space away.
What made it disband Brest then Paris before Piedmont?

Feckless: What you've detailed is the official rule, but freakflag is correct as to which one is actually disbanded.

Yup, unless the code was recently updated it's still disbanding the 1st unit in the table.

In fairness to Kestas, it's not particularly easy to find out the "distance" of a unit with so many possible paths to choose from. The easiest thing to do would be to basically hard code it, creating a three-column table with a From territory ID, a To territory ID, and a distance, if known.

The algorithm to populate this table would be something like this:
Populate the table with all entries of paired countries that are next to each other (and I know there has got to be a table for that already).
Then for all other pairs x and y, you could make a recursive function that checks all nearby countries z for x and sees if there's a complete entry in the database for z --> y; if so, the function returns that distance plus one. If there isn't a case already, then the function does the same thing looking for z --> y (though extra countries w), etc.

Once a number is returned and it is determined to be the lowest, insert this distance into the database for this pair and return (possibly resulting in more countries getting populated further up the call stack).

Once you have this table populated, then you can just use this as a quick lookup table for seeing which units are farthest from the home SCs.

I'm not sure I could write this code myself, but I think the algorithm is theoretically fairly sound.

As dangermouse said it simply deletes the first row MySQL finds; this will tend to be the oldest unit, but not necessarily (it'll be whatever is faster for MySQL)

Katsarephat; actually I already did that part just like you said, a few months back ;-)
I used a recursive graph spanning algorithm to populate the table, but the table is currently unused.

It's called pD_UnitDestroyIndex, and it has 3 columns; country, territory, unit type and index.
So England goes from (England, Armenia, Fleet, 1) to (England, London, Army, 120), and it goes by the preferred rules in the DATC :-)
But I didn't get around to hooking it up to the unit creation adjudicator and testing it (not as fun as the graph traversal algorithm itself) :-(

If anyone knows some SQL and wants to take a crack at it, it'd just be an altered DELETE query (plus some testing):
http://phpdiplomacy.net/doc/phpDoc/__filesource/fsource_GameMaster_Orders_gamemasterordersunitplacing.php.html#a113

*4 columns, that is

I'll look at it this weekend.