Query

A query is a request for information from a database or search engine. It allows users or applications to retrieve, insert, update, or delete data stored in a system. Queries can be simple, such as asking for all records in a table, or complex, involving multiple conditions, joins, and calculations.
In everyday use, typing a phrase into Google or another search engine is also considered a query. The system interprets the input, searches its index, and returns results that best match the request. Queries are the foundation of how humans and machines interact with structured and unstructured data.
Advanced
In databases, queries are often written in Structured Query Language (SQL), which standardizes how systems access and manipulate relational data. For example, SELECT * FROM customers WHERE country = 'Australia';
retrieves all customers based in Australia. Advanced queries may include nested subqueries, aggregations, and optimization techniques for faster performance.
Outside relational databases, NoSQL systems use different query languages tailored to document stores, key-value pairs, or graph data. Search engines also process queries using natural language processing (NLP), ranking algorithms, and semantic analysis to deliver the most relevant results. Optimized query performance is crucial in large-scale systems, where poorly designed queries can slow applications or overload servers.
Relevance
Applications
Metrics
Issues
Example
An e-commerce retailer used SQL queries to analyze purchase history and segment customers for a loyalty program. By refining query performance and filtering by key attributes, the company increased targeting accuracy and improved marketing ROI.