A querystring is a set of characters input to a computer or Web browser and sent to a query program to recover specific information from a database . On the Internet, a querystring (also called an HTTP querystring) is part of the set of characters automatically input in the address bar of a dynamic Web site when a user makes a request for information according to certain criteria.
In a URL (Uniform Resource Locator), the querystring follows a separating character, usually a question mark (?). Identifying data appears after this separating symbol. For example, consider the following URL:
This produces a list of all the books available from the online bookseller BookFinder4u bearing the author's name Ernest Hemingway, in reverse chronological order by publication date. The querystring in this example consists of one field or variable, technically called a key in this context (here, it is the word "sort"), followed by an equals sign (=), followed by the value for that key (here, it is the word "date"). Each key and its corresponding value, denoted as an equation, is called a key-value pair. A querystring may contain several key-value pairs. When there is more than one key-value pair, they are typically separated by ampersands (&).