Area	Data processing Databases SQL
Phase 1 (junior, mid)	• What is an index? When it is required and when to avoid? • How do you design DB schema? ◦ Whats data normalization? • What are foreign keys for? Whats referrential integrity? • What is sharding? • Whats types of database engines do you know? • How do you change database structure in production? • Can we run every API call in a huge transaction?
Phase 2 (mid, senior)	• How / why can deadlocks appear? • Whats the difference between LEFT JOIN, INNER JOIN and OUTER JOIN? • What are views for? • When one should use or not use triggers? • What is map-reduce? What is it needed for? What engines allow it? • Whats does HAVING do in SQL? • What do you know about encodings and collations?
Phase 3 (senior+)	• What do you look for in the EXPLAIN plans of your queries? • Whats the difference between Lock wait timeout and Deadlock found? • Whats a query hint? • How does UNICODE work? • What limitations of mysql do you know about? • What are isolation levels for? • How does binary tree search work?