Practice these 50 SQL questions. you can do it in 2 days if you're good with SQL concepts. don't waste more than 10 mins for each question. if you don't find an approach in 10 mins look at 4-5 discussions then think through it. if you still don't get it then look at bad solutions then try to optimize them. If you are unable to optimize then look for good solutions. https://leetcode.com/studyplan/top-sql-50/