This document doesn't replace documentation relevant to the database software you are
using, ie. README.mysql, README.pgsql or README.sqlite3.

The 'agent_id2' field.
Such field is being introduced to better support traffic matrix scenarios, where it
can be handy to have a tag to represent "qualities" of the source (say, agent_id) and
an additional one to represent "qualities" of the destination (say, agent_id2). But of
course this is only an example. The guidelines below (typically in MySQL format) are
to add such primitive to the SQL schema:

* agent_id2 field:
  - "agent_id2 INT(4) UNSIGNED NOT NULL," to declare the field itself
  - "PRIMARY KEY (..., agent_id2, ...)" to put it in the primary key 

The primitive is not declared as part of any default table version; yet will not fail
version checks which are enabled when 'sql_optimize_clauses' feature is disabled.
