Which levels survive two INNER JOINs?

Question

Accepted Answer

Each INNER JOIN requires a matching row. The first join drops anyone with no direct manager (NULL manager_id). The second join drops anyone whose direct manager has no manager of their own - so employees just one level below the top are also excluded. Only employees who are at least two levels deep in the hierarchy survive both joins. Use LEFT JOINs if you want to preserve all employees.