We subscribe to UN Comtrade and I have a particular question about
searching the database.  I have a student who is searching for "the
percent of net exports which comes from value-added manufacturing"
for both Columbia and Mexico.

I see that in Data Query Basic Selection Others, one can select
re-Export separate from Exports.  However, when I go to the
Glossary, I see re-Export defined as "exports of foreign goods in
the same state as previously imported."  However, when I look in the
definition of Exports, I see three types of exports listed,
including "(b) Domestic goods comprised of compensating products
after inward processing," which I believe represents the portion of
exports that the student wants to measure.

It is there any way to break this out in a search?  Do you keep
track of that category separately (maybe it could be retrieved in
some other way outside of Comtrade)?  If you do not, do you know of
any other entity that might be able to provide this type of data?

The question that your student asked, related to one of important issue in
International Merchandise Trade Statistics (IMTS): Goods for Processing, as
well as goods resulting from the processing (GfP). Even though, it is
recommended that GfP to be included in exports and exports, however, to
explicitly identify  (separately record) this trade may not be
internationally comparable as (a) IMTS compilers may not have adequate
sources of data (especially when inward/outward processing customs
procedures are not used), (b) national definitions of such procedures may
significantly differ.

In UN Comtrade, Export can be broken down into two: re-export and domestic
export. However, there is no further detailed break down. GfP can be part
of re-export or export (depending whether the goods resulting from the
processing change its origin or not).

I think that you should try to contact National Statistics Offices
requesting detailed breakdown on export after inward processing.