If you try to enable the tickets tags module, while using MySQL 4.x you get the following error:
ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'fields FROM ticket WHERE status != 'closed') s WHERE fields != '' ORDER BY id' at line 1")
File "/opt/trac-0.11/src/tractags/tags/0.6/tractags/ticket.py", line 66, in get_tagged_resources
The issue is that this SQL stanza
SELECT id, %s, %s AS fields FROM ticket%s
fails, because MySQL seems to think fields is a keyword. On my site I renamed fields to fieldss. Another option is using backticks ` around the field name, but I'm not sure this is compatible with other databases.