I must store inTransit information for a logistics application. My
application has a retail and wholesale side.
Items can be intransit:
from one retail location to another
from one wholesale location to another
from a retail location to a wholesale location
from a wholesale location to a retail location

I have a table for retail locations and a table for wholesale
locations. These entities work different in the business process and
have different attributes so I think they should be modeled as
separate entities.

How should I physically implement this?

I see 4 solutions:
1) The inTransit table has 2 columns for the FROM location and 2
columns for the TO location. Ex. to_retail, to_wholesale,
from_retail, from_wholesale.
The drawbacks of this approach are that I have no way to enforce that
only 1 TO column and 1 FROM column have values. It is also not very
easy to add a new location type if one is needed.

2) Have 4 version of the inTransit table. One for retail to retail,
one for retail to wholesale, etc.
The drawback is that when retrieving data I have to join 4 tables to
find out what is in transit. Also, if a new type is discovered I'll
have to add tables and update all of my SQL.

3) Have 1 inTransit table with 1 FROM column and 1 TO column. In
addition, I'll have type columns for each location. If the FROM_type
= 'Retail' I'll join to the retail table.
The drawback here is that I have mixed metadata with data. I also
think the SQL will be a problem because I'll have to join with a table
that is determined by the data. It can be done but performance may
suffer.

4) Move the locations into one table with a type column. Then my
intransit table only needs the to and from locations.
The drawback to this approach is that I will need columns that are not
used for some types. Of course I could break them out into another
table but then I'll have this question on that table.

I would appreciate any advice you can give me.