To interrogate a collection of data such as records in a database. The term may also be used to search a single file or collection of files such as HTML files on the Web. However, 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 on the Web yields only a list of matching 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.
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.
 | Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2008 The Computer Language Company Inc. All rights reserved. |
Additional Resources
- Dicm PACS Service (zip)
- Dicm PACS Service receives and saves DICOM files from DICOM enabled devices such as Ultrasound Machines, CT Scanners, MR machines, C-ARMS, X-Ray Machines, and Film Scanners. DICOM clients download files via DICOM query-retrieve. Dicm PACS Service operates as a console application for easy configuration and debugging.This version is the first...
- Software downloads 2008-08-26
- Exploit code published for Apache Tomcat flaw
- The United States Computer Emergency Response Team (US-CERT) has raised an alarm for a serious vulnerability in Apache Tomcat, warning that a proof-of-concept exploit is publicly available. The code, posted to Milw0rm.com, exploits a directory traversal vulnerability vulnerability in the way Apache Tomcat handles malformed requests. ...
- Blog posts 2008-08-21
- Reader Poll: Which mouse should I choose?
- So just yesterday as I was gearing up to offer you a nice slice of Toybox goodness via my laptop, my trusty old Logitech V320 Cordless Optical mouse zapped out, ne'er to return. Ouch. The problem was not Logitech's -- I've been using their...
- Blog posts 2008-08-21
- Open Source, Dtrace, and tuning
- Open Source, Dtrace, and tuningComment.I knew a guy who only drove old Renaults. He did this, because he knew he could fix them. The cars had presented him many occaisions on which he was able to prove this.I, on the other hand, drive Audis, because I beleive I'll never have...
- Discussion threads 2008-08-21
- Fortune 500 companies use of email spoofing countermeasures declining
- Here's a paradox - a technology originally meant to verify the sender of an email message for the sake of preventing spoofed messages from reaching the network, still hasn't been embraced by the world's biggest companies despite being around for years, but is actively used by adaptive spammers increasingly abusing...
- Blog posts 2008-08-19
- Search engines under the spotlight this week
- I'm spending most of this week at the Intel Developer's Forum but also wanted to give some time to another show happening in the Bay Area this week: Search Engine Strategies, being held at the San Jose Convention Center in Silicon Valley. Monday was one of those unofficial days of...
- Blog posts 2008-08-18
- Searching by color to nibble away at Google.
- Searching by color to nibble away at Google.Must be a slow news day...The reality is, anyone who wants to create such a tool USING Google's index can do so using Google Custom Search. In fact, many are.The fact that someone COULD make a custom search engine using their own...
- Discussion threads 2008-08-18
- .NET 3D Visualization Tool Package (zip)
- .NET 3D visualization Tool Package is an easy-to-use and powerful .NET component used on Windows Form platform for development of .NET 3D graphics applications including scientific visualization, 3D game, and CAD applications. General commands such as rotate, zoom, pan, selection,and query are pre-defined for saving your coding time. 2D and...
- Software downloads 2008-08-18
- Top search query generators in UK in June 2008
- Domain June-08 May-08 June-07 Search Engine June-08 May-08 June-07 Google Properties 87.34% 87.30% 79.48% Google Search 87.81% 88.91% 78.55% Yahoo! Properties 4.00% 4.09% 7.67% MSN Search 6.72% 5.52% 14.68% Microsoft Properties 3.72% 3.72% 5.74% Yahoo! Search...
- Blog posts 2008-08-17
- William Shatner signs off on video autographs
- Customers of Live Autographs get not just a signed photograph, book or napkin; they receive a customized video clip with a short personal message from the star. LOS ANGELES--William Shatner sat in a drab office staring at a TV monitor displaying a message he was supposed to read to...
- News items 2008-08-15
- Navicat (Oracle GUI) (exe)
- Navicat Oracle GUI is an Oracle database management tool, which can convert XML, CSV, MS Excel, MS Access, and popular data formats to MySQL databases, eliminating time-consuming data entry and the errors that accompany it. Other useful major features include Import and Export wizard, Unicode support, SSH Tunnel, Batch Job...
- Software downloads 2008-08-15
- Psystar requires Acknowledgement of Sale letter to receive restore media
- Psystar requires Acknowledgement of Sale letter to receive restore mediaAsking customers ...... to fill in a form and enter their credit card details to get a FREE UPDATE when that could be put on the website ...... yeah, smells awfully dodgy to me.RE: Psystar requires Acknowledgement of Sale letter to...
- Discussion threads 2008-08-14
- Psystar requires Acknowledgement of Sale letter to receive restore media (updated 3x)
- Psystar sent an email late yesterday to all customers of their Mac-compatible Open Computer with a subject of "Open Computing Restore Delivery" or "Open Computing Restore Media." The email says, in part: Thank you for purchasing one of our Open Computing products. We at Psystar are...
- Blog posts 2008-08-14
- Measuring (not so) recent BIND nameserver patching
- Guest editorial by Derek Callaway This post is meant to provide an approximation of BIND nameserver updates that occurred during the past month, most likely in response to Dan Kaminsky's DNS cache poisoning vulnerability. I conducted this research because I was curious as to how widely BIND...
- Blog posts 2008-08-14
- Bill Gates: Software innovation poses privacy challenge
- Bill Gates told a Hong Kong gathering that society will need more explicit rules governing privacy boundaries around software as the mobile/PC line blurs. As software gets more powerful, privacy issues pose "an interesting software challenge", said Microsoft Chairman Bill Gates. Recounting a short history of software...
- News items 2008-08-14
- 1099 Pro Professional Edition (exe)
- The 1099 Pro Professional Edition is the easiest and most advanced software for all your paper filing needs. It produces all forms in the 1099, 1098, and 5498 series. It also prints to plain paper, preprinted forms, and continuous forms. Complimentary technical support. Query wizards for printing and viewing of...
- Software downloads 2008-08-13
- The Future of the Web
- The semantic web can be quite a hard concept to grasp when discussed in an abstract way: the above video is a particularly useful, clear exposition of the enormous promise and power the future of knowledge sharing holds. Parallax, a novel browsing interface designed by David Huynh...
- Blog posts 2008-08-12
- Putting Semantic Technology to work at BT
- UK-based telecoms and more provider, BT, has been interested in the Semantic Web for a long time, as a brief conversation I recorded with the company's Head of Next Generation Web Research back in January 2007 illustrates. John Davies appears in silicon.com this week, as part of...
- Blog posts 2008-08-12
- SqlToTxt (exe)
- SqlToTxt is a tool to export SQL Server data to file (csv, text, sql, xml, html, and excel). Main features: Export Sql Server data to multiple formats file: txt, csv, xml, html, sql, and Excel; Export a single table data, export all tables data in a schema, export data from...
- Software downloads 2008-08-08
- Google gives us the keys to insightful information
- If you are someone who can't get enough data, Google's new "Insights for Search" (which I'm sure will be renamed to simply "Google Insights" when they realize the current name is too long) is going to be a place that you want to visit. Google Insights for...
- Blog posts 2008-08-06
Neighboring Terms
Premier Vendor Content Whitepapers, webcasts & resources from our Power Center Sponsors
- Access the latest Intel and industry best practices
-
Designed specifically to address the concerns of senior IT managers at organizations with more than 100 employees, the Intel Premier IT Professional Program provides best practices via local and e-Seminars and a members-only Web site.
- View the Intel Premier IT Professional web-site tour >>
- Visit the all new ZDNet Enterprise Mobility Hub sponsored by Verizon Wireless. It has the latest news, commentary, and resources for your mobile strategy development.
- Read the latest from Matthew Miller's The Mobile Gadgeteer Blog
- Five steps to protect mobile devices anywhere, anytime
- Watch a video about Distributed Antenna Systems (DAS)
- Learn how you can fetch your email from anywhere
- All this and more on the ZDNet Enterprise Mobility Hub
