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Query languages, data query languages or database query languages (DQLs) are computer languages used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL).
Broadly, query languages can be classified according to whether they are database query languages or information retrieval query languages. The difference is that a database query language attempts to give factual answers to factual questions, while an information retrieval query language attempts to find documents containing information that is relevant to an area of inquiry.
- Atomese, the graph query language for the OpenCog graph database, the AtomSpace.
- Attempto Controlled English is a query language that is also a controlled natural language.
- AQL is a query language for the ArangoDB native multi-model database system.
- .QL is a proprietary object-oriented query language for querying relational databases; successor of Datalog;
- Contextual Query Language (CQL) a formal language for representing queries to information retrieval systems such as web indexes or bibliographic catalogues.
- CQLF (CODYASYL Query Language, Flat) is a query language for CODASYL-type databases;
- Concept-Oriented Query Language (COQL) is used in the concept-oriented model (COM). It is based on a novel data modeling construct, concept, and uses such operations as projection and de-projection for multi-dimensional analysis, analytical operations and inference;
- Cypher is a query language for the Neo4j graph database;
- DMX is a query language for data mining models;
- Datalog is a query language for deductive databases;
- Discovery Query Language is a query language for accessing Watson Discovery Services on IBM Cloud;
- EdgeQL is a declarative graph-relational query language of EdgeDB 
- F-logic is a declarative object-oriented language for deductive databases and knowledge representation.
- FQL enables you to use a SQL-style interface to query the data exposed by the Graph API. It provides advanced features not available in the Graph API.
- Gellish English is a language that can be used for queries in Gellish English Databases, for dialogues (requests and responses) as well as for information modeling and knowledge modeling;
- Gremlin is an Apache Software Foundation graph traversal language for OLTP and OLAP graph systems.
- GraphQL is a data query language developed by Facebook as an alternate to REST and ad-hoc webservice architectures.
- HTSQL is a query language that translates HTTP queries to SQL;
- ISBL is a query language for PRTV, one of the earliest relational database management systems;
- Jaql is a functional data processing and query language most commonly used for JSON query processing;
- JSONiq is a declarative query language designed for collections of JSON documents;
- KQL is a query language used in Azure Data Explorer (Kusto) and the CMPivot tool in Microsoft System Center Configuration Manager
- LINQ query-expressions is a way to query various data sources from .NET languages
- LDAP is an application protocol for querying and modifying directory services running over TCP/IP;
- LogiQL is a variant of Datalog and is the query language for the LogicBlox system.
- MQL is a cheminformatics query language for a substructure search allowing beside nominal properties also numerical properties;
- MDX is a query language for OLAP databases;
- N1QL is a Couchbase's query language finding data in Couchbase Servers;
- OQL is Object Query Language;
- OCL (Object Constraint Language). Despite its name, OCL is also an object query language and an OMG standard;
- OPath, intended for use in querying WinFS Stores;
- OttoQL, intended for querying tables, XML, and databases;
- Poliqarp Query Language is a special query language designed to analyze annotated text. Used in the Poliqarp search engine;
- PQL is a special-purpose programming language for managing process models based on information about scenarios that these models describe;
- PTQL based on relational queries over program traces, allowing programmers to write expressive, declarative queries about program behavior.
- QUEL is a relational database access language, similar in most ways to SQL;
- RDQL is a RDF query language;
- Rego is a query language inspired by Datalog;
- ReQL is a query language used in RethinkDB;
- SMARTS is the cheminformatics standard for a substructure search;
- SPARQL is a query language for RDF graphs;
- SPL is a search language for machine-generated big data, based upon Unix Piping and SQL.
- SCL is the Software Control Language to query and manipulate Endevor objects
- SQL is a well known query language and data manipulation language for relational databases;
- SuprTool is a proprietary query language for SuprTool, a database access program used for accessing data in Image/SQL (formerly TurboIMAGE) and Oracle databases;
- TMQL Topic Map Query Language is a query language for Topic Maps;
- TQL is a language used to query topology for HP products
- Tutorial D is a query language for truly relational database management systems (TRDBMS);
- U-SQL is a data processing language invented at Microsoft
- XQuery is a query language for XML data sources;
- XPath is a declarative language for navigating XML documents;
- XSPARQL is an integrated query language combining XQuery with SPARQL to query both XML and RDF data sources at once;
- YQL is an SQL-like query language created by Yahoo!
- Search engine query languages, e.g., as used by Google or Bing
- Norbert E. Fuchs; Kaarel Kaljurand; Gerold Schneider (2006). "Attempto Controlled English Meets the Challenges of Knowledge Representation, Reasoning, Interoperability and User Interfaces" (PDF). FLAIRS 2006.
- "Getting Started with Querying". IBM. Retrieved July 29, 2020.
- ""EdgeQL documentation".
- "FQL Overview". Facebook Developers. Archived from the original on 2013-12-18. Retrieved 2013-12-11.
- http://gellish.wiki.sourceforge.net/Querying+a+Gellish+English+database[permanent dead link]
- "Search operators". Google Inc. Retrieved August 22, 2015.
- "Bing Query Language". Microsoft. Retrieved August 22, 2015.