SQl

SQL (Structured Query Language) is a domain-specific language for managing relational databases. It enables querying data, inserting and updating records, modifying schemas, and controlling access. SQL is declarative: users specify the desired result and let the database optimize the execution plan.

SQL originated at IBM in the 1970s, based on relational algebra and initially called SEQUEL. It was standardized by ANSI in 1986 and by ISO soon after. Today, it underpins most relational databases, with vendor-specific extensions.

The language comprises sublanguages: DDL (CREATE, ALTER, DROP), DML (SELECT, INSERT, UPDATE, DELETE), DCL (GRANT, REVOKE) and TCL (BEGIN, COMMIT, ROLLBACK). The central operation is querying via SELECT, often with joins, grouping, and ordering. Other features include constraints, views, indexes, stored procedures, and triggers.

Although SQL is standardized, implementations vary. The ANSI/ISO core is augmented by vendor-specific extensions (for example, PL/SQL in Oracle, T-SQL in Microsoft SQL Server, PL/pgSQL in PostgreSQL). Differences occur in data types, functions, and syntax for limits and joins.

SQL remains essential for relational data management, supporting analytics, reporting, and application back ends. It commonly uses parameterized queries to mitigate injection risks and relies on transactions for data integrity. Its suitability declines with unstructured data and non-relational stores.