> For the complete documentation index, see [llms.txt](https://docs.serverlessapigateway.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.serverlessapigateway.com/glossary/q/query-language.md). # Query Language A query language is a specialized programming language designed for retrieving and manipulating data stored in databases or other data management systems. Query languages provide a structured way to express requests for specific data, filtering criteria, sorting orders, and aggregation operations. SQL (Structured Query Language) is the most widely used query language, designed for relational databases like PostgreSQL, MySQL, and SQL Server. It provides commands for selecting, inserting, updating, and deleting data, as well as defining schemas and managing access. NoSQL databases use their own query mechanisms, such as MongoDB's query documents or DynamoDB's key-condition expressions. In the API context, GraphQL functions as a query language for APIs, allowing clients to specify exactly which data fields they need. API gateways can interact with query languages in several ways: translating incoming API requests into database queries, caching query results, and enforcing query complexity limits to prevent expensive queries from overloading backend databases. Some gateways support direct database-to-API mapping, automatically generating API endpoints from database schemas. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.serverlessapigateway.com/glossary/q/query-language.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.