First-round SQL screens test the basics quickly: filtering, grouping, joins, NULLs and the difference between WHERE and HAVING. Most are short queries against tables you see for the first time, and a few are questions about how SQL behaves.
Treat each one like the real thing. Look at the tables first, say to yourself what one row of the answer is, then write the simplest query that returns it. In a live interview, talk through the edge cases too: what happens with NULLs, ties or rows that don't match.
These questions are written for this site and use Kestrel's tables.