Data+Querying

Definition
Data querying is the process of asking questions of data in search of a specific answer.

Description
Unlike many forms of search (i.e. Google), queries are normally structured and require specific parameters or code, known as SQL (Structured Query Language). A query could be written to answer questions like, "How many items were sold in Region 2 last month?" Queries are one of the things that make databases so powerful. A "query" refers to the action of retrieving data from your database. Usually, you will be selective with how much data you want returned. If you have a lot of data in your database, you probably don't want to see everything. More likely, you'll only want to see data that fits a certain criteria.

For example, you might only want to see how many individuals in your database live in a given city. Or you might only want to see which individuals have registered with your database within a given time period.

As with many other tasks, you can query a database either programatically or via a user interface.

Specific examples

 * Attributes of query tool:
 * Cross-Browsing of Dimension Attributes - A real dimension table, such as a list of all of your products or customers, takes the form of a large dimension table with many, many attributes (fields). It is absolutely mandatory for a query tool to present, in real time, a list of the valid values in a dimension attribute (for example, product brand) and let the user choose one or more of the values to set a constraint. This basic browsing capability is now fairly standard in sophisticated query tools. Cross-browsing, on the other hand, refers to the capability of a query tool to present the valid values of the product brand, subject to a constraint elsewhere on that dimension table.
 * Open Aggregate Navigation - Aggregate navigation is the ability to automatically choose pre-stored summaries, or aggregates, in the course of processing a user's SQL requests. Aggregate navigation must be performed silently and anonymously, without the end user or the application developer being aware that the aggregations even exist. Open aggregate navigation occurs when the aggregate navigation facility is a separate module that is available for all query tool clients simultaneously.
 * Multipass SQL - Breaking a single complex request into several small requests is called multipass SQL. Multipass SQL also allows drilling across several conformed data marts in different databases, in which the processing of a single galactic SQL statement would otherwise be impossible.
 * Semi-Additive Summations - There is an important class of numeric measures in common business fact tables that are not completely additive. Anything that is a measure of intensity is generally not additive, especially across the time dimension.
 * Show Me What Is Important - your query tools must help you automatically sift through the data to show you only what is important. At the low end, you simply need to show data rows in your reports that meet certain threshold criteria.
 * Behavioral Studies - An interesting class of applications involves taking the results of a previous report or set of reports and then using these results over and over again at a later time.

Additional contributions
this video shows what is SQL and relational database:

Resources

 * Krehel, G. A. (2001). //U.S. Patent No. 6,208,985 //. Washington, DC: U.S. Patent and Trademark Office.
 * Comito, C., Gounaris, A., Sakellariou, R., & Talia, D. (2009). A service-oriented system for distributed data querying and integration on Grids. //Future Generation Computer Systems //, //25 //(5), 511-524.