Code review comment for ~cjwatson/launchpad:db-bugsummary-statement-triggers

During the review I wanted to see if a few changes in approach were viable, but ended up going further than expected and wound up with a solution that is structured a bit differently, and doesn't use any dynamic queries at all: https://paste.ubuntu.com/p/SQzFYMBBqZ/

Thoughts on that?