On the left is a quick export generated by dbVisualizer. This is just tables and columns; there are no enforced relational integrity constraints at the database levels.
On the right is a diagram of the relationships between tables, generated from the schema.dot file which ships with RT 4 under the docs/ directory.
Look at the file 'docs/rt-schema-relationships.dot', included in the RT 3.x distribution (download page: http://www.bestpractical.com/rt/download.html ).
Or, browse http://svn.bestpractical.com/cgi-bin/index.cgi/bps/browse/rt/branches/ , choose the link to the relevant RT version, then click on the 'docs' link, then on 'rt3-schema-relationships.dot'.
How to visualize 'dot' format Edit
- dbdesigner4, see http://www.fabforce.net/dbdesigner4/ (sooner or later will be MySQL Workbench. See: The FabForce Forum)
- graphviz, see http://www.research.att.com/sw/tools/graphviz/
Existing visualizations Edit
(Warning: these may be out of date. You can always download dotty or other visualizer and apply it to your .dot file to see the latest).