Databases

Relational and NoSQL database concepts essential for system design and backend interviews.

Topic	Key Focus
SQL Fundamentals	JOINs, Subqueries, Aggregations, Window functions
Indexing	B-Tree, Hash index, Composite, Covering index
Transactions & ACID	Isolation levels, Locking, MVCC
Normalization	1NF through BCNF, Denormalization trade-offs
NoSQL Overview	Key-value, Document, Column-family, Graph
Query Optimization	EXPLAIN plans, Index tuning, Query rewriting