query

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query

[′kwir·ē]
(computer science)
A computer instruction to interrogate a data base.

query

(database, information science)
A user's (or agent's) request for information, generally as a formal request to a database or search engine.

SQL is the most common database query language.

query

(character)

query

To search for data. In addition to obtaining lists of records that match the search criteria, queries to a database allow for counting items and summing amounts. A query to a search engine such as Google or Bing yields a summary of the contents of Web pages and is more often called a "search."

For years, query and report programs have been the primary applications that produce output from information systems. A query implies an online request as required (look up that record), while a report implies a more elaborate printout with page headings and numbers that is typically produced at regular intervals such as end of month. See report writer.

Simple or Complex
Defining a query for a relational database can be extremely simple or very complex. If the query is based on one matching condition, such as "retrieve all customers who owe us more than $10,000," it is usually easy to define in a query language or program. However, "retrieve all customers who owe us more than $10,000 from purchasing toasters" is not easy. It requires several steps to determine how many toaster orders are in the balance due.

Tables Must Be Joined
Relational databases are designed to eliminate redundancy. The goal is to store a data item in one table and not have it duplicated in others. For example, an order record will contain the product number ordered, but often not its description. The description is stored in a product table. Thus, any printout of products ordered and their descriptions requires that the order table be linked to the product table for that query or report. Linking customer, order and product tables is a common example of "joining" tables to satisfy a query.

Contents of a Query
Most queries require at least the following conditions to be stated. First, which table or tables is the data coming from. If from two or more tables, what is the link between (typically account number or name). Next, define the selection criteria, which is the matching condition or filter. Lastly, define which fields in the tables are to be displayed or printed in the result. See SQL.


The Query Statement
This diagram depicts the typical conditions that have to be stated when querying a relational database.
References in periodicals archive ?
Neo4j, a NO-SQL graph database is used which results in high query performance on complex data and uses cypher a declarative graph query language for expressive and efficient querying and updating of graph.
In this work, we combine the concept of collaborative querying and graph visualization, leveraging on the individual strengths of both techniques to help users better formulate their queries within an IR system.
When the National Practitioner Data Bank opened in September 1990, the reporting and querying of malpractice payments and adverse actions primarily against physicians were the only reportable actions.
SQL has remained the most enduring standard querying language for stored data over three decades due to its combination of powerful data processing primitives, functionality, power, and relative ease-of-use," said Dr.
The book serves as a new resource to help developers, architects, and managers learn and assess XML querying capabilities to find and extract fine-grained information from large content repositories.
Consequently, several vendors -- including Microsoft with its LINQ project -- are seeking to break down the barriers between non-native APIs and the programming language on top of it, by allowing querying in native language -- an approach that could become popular to access databases from OO programming environments.