Query

What is a Query?

A query is a request that is asked in a formal manner. For example, relational databases require the use of a formal structured query language (SQL) to retrieve, modify, or manipulate data. Every query in SQL must be written according to specific syntax rules and logically constructed to produce the desired result.

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When you request something from a search engine or some other data retrieval system, you’re forming a query. This request is then processed by the system, which returns the information or results that match your query criteria.

Techopedia Explains the Query Meaning

Techopedia Explains the Query Meaning

Query definitions can have nuances, and query meanings can change depending on the context in which the term is used. In everyday language, a query is simply a general request for information. In computing, a query is a structured way to access information from an information system so it can be used or modified.

In the context of databases, queries are precisely formulated requests. In the context of search engines, queries are what a user types into the search box. In the context of programming, queries are application programming interface (API) calls or commands for action.

How Query Works

Queries provide users, applications, and data sources with a way to communicate with each other.

  1. The process begins by specifying what information or action is desired. In everyday use, this could be as simple as asking a question. In more technical contexts, this usually involves using specific commands or programming keywords that the specific data retrieval system understands.
  2. Once the query is formulated, it is submitted to the system from which the information is sought. This step might require entering a search term into a search engine, executing an SQL command in a database management system (DBMS), or asking a digital AI assistant a question.
  3. The system receiving the query will then process it to understand what is being asked. This involves parsing the query, interpreting its intent, and determining the best way to process the request.
  4. After processing the query, the system will retrieve the relevant information or perform the requested action.
  5. Finally, the information or outcome of the action will be presented to the user or application program that made the request.

The effectiveness of this process depends on several factors, including the precision of the query, the system’s ability to interpret and process the query, the quality of the data that are available for query response, and the ability of the data retrieval system or software component to perform a specific task.

Common Query Languages

Structured query language is the standard language for managing and manipulating data in relational databases. It is used for a variety of CRUD operations including data retrieval, data insertion, data update, and data deletion.

Each query in SQL must be written according to specific rules. The rules are designed to ensure that queries are both precise in their intent and interpretable by the database system.

Although SQL is by far the most common and widely used language for interacting with databases, there are a number of other query languages that are used for different applications and data systems.

They include:

NoSQL Languages
Syntax will vary depending on the specific NoSQL database system.

SPARQL
Used to query and manipulate Resource Description Framework (RDF) data.

XPath
A query language for selecting nodes from an XML document. Often used in conjunction with XSLT.
Gremlin
Used to query other types of graph databases.
Lucene Query Language
Used with Apache Lucene and systems built on Lucene like Apache Solr.
DAX
A formula language for querying Microsoft data analysis tools.
MDX
Used to query online analytical processing (OLAP) databases for business intelligence and data analysis purposes. 

Types of Queries

The number and variety of query languages reflect the different ways data can be stored, retrieved, and manipulated across different domains.

Types of queries include:

  • Data retrieval queries that fetch specific information from a data source.
  • Data modification queries that change existing data.
  • Data deletion queries that remove records.
  • Data aggregation queries that calculate summaries or statistics.
  • Simple filtering queries that select data based on specific criteria.
  • Grouping and aggregation queries that summarize data across categories.
  • Complex calculation queries that perform statistical or mathematical operations on data.
  • Pattern-matching queries that find data that matches specific patterns or trends.
  • Structural queries that focus on the relationships and organization of the data itself.
  • Text-based search queries that use keywords or natural language processing (NLP) to find relevant information.
  • Specialized queries designed for domain-specific analysis in fields like science or finance.

How to Perform a Database Query

Performing a database query involves requesting the database system to perform a specific action. Before you can submit a query, however, you’ll need to establish a connection to the database where the data you need is stored.

Once you have access, you will need to think about what you want to request. For example, your query could be as simple as asking for a list of all book titles on a specific topic. Or it could be as complex as requesting the average number of pages for books published in the past year by genre.

The next step is to write your request in a language the database understands and then submit it. This is typically done through a database management system user interface or a runtime library designed for database interactions.

The database engine will then analyze the query to understand the request and execute the query.

Query Examples

Here are four examples of queries that are formulated for different purposes.

The first example is an SQL query to retrieve titles and authors of books classified by biography.

example is an SQL query to retrieve titles and authors of books classified by biography

The second example is a search engine query to retrieve biographies on the New York Times best-seller list.

second example is a search engine query to retrieve biographies on the New York Times best-seller list

The third example is an API call that requests an alert when the New York Times publishes a new best-seller list.

third example is an API call that requests an alert when the New York Times publishes a new best-seller list

The fourth example is a voice search query that asks a digital assistant to identify the title of Alec Nevala-Lee’s biography about Buckminster Fuller.

fourth example is a voice search query that asks a digital assistant to identify the title of Alec Nevala-Lee’s biography about Buckminster Fuller.

The Bottom Line

Queries allow users and systems to communicate with databases, web content, and other information sources.

The ability to formulate and execute queries accurately is an important skill that allows end users to find the information they need; data analysts to extract insights and translate data into actionable intelligence; and developers to build applications and websites that facilitate the global exchange of information.

FAQs

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.