kyselykieli

Kyselykieli (fromFinnish kysely meaning "query" and kieli meaning "language") is a formal language used to express data retrieval and manipulation requests to a database or other data source. It is typically declarative, focusing on what data is needed rather than how to compute it, and is distinguishable from general-purpose programming languages by its emphasis on data access over imperative control flow.

In Finnish technical literature, kyselykieli is used as a generic term for any language designed to query data. The most widespread example in relational database systems is SQL (Structured Query Language). Other widely used query languages include SPARQL for RDF data, GraphQL for APIs, and XQuery for XML. NoSQL systems often implement their own query languages or provide domain-specific query DSLs.

A typical kyselykieli defines syntax and semantics for retrieving and sometimes modifying data, often including capabilities such as filtering, projection, joining, aggregation, and sorting. Many languages also support data definition or data manipulation features (DDL/DML), transaction semantics, and hooks for optimization by a database engine. Queries are translated by the engine into execution plans and executed against stored data, potentially using indexes to improve performance. Security considerations, such as access control and protection against injection attacks, are central to their practical use.

Kyselykieli remains a foundational concept in data management, underpinning how users and applications specify precise data requirements and interact with diverse data stores across relational, semi-structured, and API-based systems.