queries

A query is a formal request for information from a data source. In computing, queries specify criteria and operations that select, compute, or transform data. Queries can target databases, search engines, data warehouses, or knowledge bases, and they are central to most data-driven applications.

Database queries: In relational databases, queries are written in languages such as SQL. A typical query specifies what data to retrieve, from which tables, and under what conditions, and may include grouping, aggregation, and sorting. Other data models use specialized query languages, including SPARQL for RDF graphs and XQuery for XML. A query may be evaluated by the database engine using an execution plan that determines access paths, joins, and operations. Indexes, statistics, and query optimization techniques are used to improve response time.

Search and information retrieval: A search query is a user-produced string of keywords used to locate documents or records. Engines interpret the query, often applying natural language processing, synonyms, stemming, and stop-word removal. Results are ranked by relevance and may be refined with filters, facets, or advanced operators such as boolean logic, phrase queries, or wildcard characters.

Other query styles: APIs may expose query capabilities such as GraphQL for selectively retrieving fields from an API, or SPARQL for querying knowledge graphs. Queries are foundational to data access, discovery, and analytics across many domains.