Challenge 53 · Backfill a column on a live table with no write lock

The brief

The submission

tests passed 8/8
time taken 00:48
10/10 — hints used 0

Where it came from

A draft with no fix attached: the project, licence, issue and fixing commit that would credit it are not all recorded yet, so it cannot be published and nothing can be graded against it. Publishing also needs a person to review it.