Databases & SQL interview prep

• Concurrency Control — How a database lets many transactions run at once without corrupting data: locks and two-phase locking, optimi
• Consensus Algorithms — How a group of machines agrees on one ordered log even when some of them crash: majorities, Raft, Paxos, safet
• Database Recovery — How a database keeps committed data through crashes, disk loss and human error: the write-ahead log, checkpoin
• DDL & DML — Define tables with constraints (CREATE, ALTER, DROP), change rows safely (INSERT, UPDATE, DELETE, upsert), and
• Indexing Deep Dive — How database indexes work and when they help: B-tree internals, scan types, composite column order, covering,
• Interview Problems: Easy — The easy SQL problems that open most interviews: second-highest value, duplicates, rows with no match, day-ove
• Interview Problems: Hard — Hard SQL problems combine two or three techniques: top N per group, medians, running totals, gaps and islands,
• NewSQL and Distributed SQL — How Spanner, CockroachDB and TiDB keep SQL and ACID transactions while spreading data over many machines: rang
• NoSQL Internals — How the four NoSQL families store, spread and copy data, shown through DynamoDB, MongoDB, Cassandra and Neo4j,
• Partitioning & Sharding — How to split a large dataset into pieces: range, hash and directory partitioning, choosing a shard key, fixing
• Replication Strategies — How databases keep copies of data on several machines: one leader, many leaders or no leader, synchronous or a
• Set Operations — UNION, UNION ALL, INTERSECT and EXCEPT stack or compare the rows of two queries. Know how each treats duplicat
• Specialized Databases — Time-series, search, vector and spatial databases: the special index each one is built around, how it works, a
• SQL Fundamentals — The building blocks of every query: SELECT, WHERE, GROUP BY, HAVING, ORDER BY and LIMIT, the order they run in
• SQL Isolation Levels — What each isolation level promises, which anomalies slip through (dirty reads, lost updates, read skew, phanto
• SQL Joins — INNER, LEFT, RIGHT, FULL, CROSS and self joins: which rows each keeps, where NULLs appear, and the traps that
• Storage Engines — How a database lays data out on disk and in memory: pages, B-trees, heaps and clustered indexes, the buffer po
• Subqueries & CTEs — Queries inside queries: scalar and correlated subqueries, IN and EXISTS, derived tables, WITH clauses, and rec
• Transaction Management — How a database makes a group of changes all-or-nothing and durable: ACID mechanisms, commit and the write-ahea
• Window Functions — ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD, running totals and moving averages: calculations across related rows

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