SQL

You don’t need a full DBA degree to pass SQL parts in tech interviews.

Just work through the SQL 50 collection on Leetcode — it's more than enough to cover your needs.

Practice writing queries without peeking at answers too soon. A lot of interviewers want to see your thinking, not just the final output.

Be comfy with small tweaks like changing JOINs or adding WHERE conditions fast. Interviewers love throwing small changes mid-question.

Also, if you're just starting from scratch, here are two fantastic resources: Интерактивный тренажер по SQL on Stepik — an awesome free hands-on course to get you rolling. And LearnDB — a super practical deep dive if you want to get serious fast.