I think the fact that these linking key values originate from an external database is immaterial, no? The idea is I have a guaranteed unique field on one record type that has a legitimate matching key linking it to another record type. Just like NS has for 'native' joins via internal id - only I seek to do the linking on a custom field that I know is valid as PK/FK between the tables.

But, you could build a custom solution to link these together

The best way, I think, would be to synchronize that primary table into netsuite through some integration (Restlet, Suitelet, or SuiteTalk).

Then, you could store the reference to the NEtSuite internal record type instead. This would be joinable in workbooks, just as you wish.

I have done something like this, and have some record types that simply mirror an external table and a small subset of fields

The other option would be to create a custom linking record type with three fields: the external key, and two List/Record fields referring to the records you want to link. You'd need to create a Map/Reduce or Scheduled script to perform two independent searches, then match the results together, storing them in the linking table. You could then build searches off of that linking table combining values from both records.

If you don't mind using an external tool for queries, I do recommend using the JDBC or ODBC driver. It gives you the ability to write standard SQL queries, joining on any arbitrary fields just as you need to. It really depends upon what you are trying to do.

so far, the actual code for doing typical queries is far more complicated looking with

N/query

than the old query filter expression syntax and column specifications in plain

N/search

the fact that you can do parent-child joins or child-parent joins is nice though, meaning you can join two records related to the same record, which definitely was not possible before.