Second-round SQL questions add one step to the basics: rank inside a group, compare with the previous row, find duplicates after cleaning, or turn counts into a percentage without losing the decimals. Interviewers also ask why one approach is better than another.
Work each one in the order you'd explain it aloud: what one row of the answer is, which tables, which window or grouping, then the edge cases (ties, NULLs, whole-number division). All questions are written for this site and use Kestrel's tables.