SQL
Structured Query Language for managing relational databases. Tables, rows, columns, and powerful joins to query related data.
What is SQL?
Structured Query Language for managing relational databases. Tables, rows, columns, and powerful joins to query related data.
SQL is a foundational concept that sits in the Database Fundamentals area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "SQL" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn SQL in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the SQL lessonRelated lessons
Lessons that touch on SQL as part of a larger topic.
NewSQL Databases
Distributed SQL databases that promise the scalability of NoSQL with the ACID guarantees of traditional SQL. CockroachDB, Google Spanner, and the NewSQL movement
intermediate · database types storage
SQL vs NoSQL
Database model comparison, relational vs non-relational data stores
foundation · core fundamentals
Apache Ignite
Distributed cache meets SQL engine, when you need to query your cache, not just look up keys
foundation · caching strategies
Parameterized Queries
The complete defense against SQL injection, separating SQL structure from user data
intermediate · security architecture
Prepared Statements
Pre-compiled SQL templates that combine security with performance, parse once, execute many times
intermediate · security architecture
See also
Related glossary terms you might want to look up next.
NoSQL
Databases that don't use traditional table-based relational models. Includes document stores, key-value, graph, and column-family databases.
Database
An organized collection of data that can be easily accessed, managed, and updated. The backbone of almost every application.
ACID
Four guarantees for database transactions: Atomicity (all or nothing), Consistency (valid states only), Isolation (no interference), Durability (changes persist).