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SQL (Structured Query Language) is a domain-specific language designed for managing and querying data stored in Relational Database Management Systems (RDBMS). It was developed at IBM by Donald D. Chamberlin and Raymond F. Boyce in the early 1970s, standardized as ANSI SQL in 1986, and has been the universal language of databases ever since. Every major database — MySQL, PostgreSQL, Oracle, Microsoft SQL Server, SQLite — speaks SQL with minor dialect differences.

A relational database stores data in tables — structured rows and columns, like a very powerful spreadsheet. Tables relate to each other through keys. A customers table links to an orders table via a customer_id. SQL is the language you use to create these tables, insert data into them, query and filter data, update records, delete records, and define relationships between tables. It is declarative — you describe what you want, and the database engine figures out how to retrieve it efficiently.

The problem SQL solves is structured data retrieval at scale. An e-commerce platform may have 10 million products, 50 million customers, and 200 million orders. SQL lets you ask precise questions of this data — 'which customers in Bangalore spent more than ₹10,000 in the last 30 days?' — and get answers in milliseconds, because the database query optimizer creates an efficient execution plan automatically. No other tool gives you this combination of expressiveness and performance for structured data.