Category:Databases

From Uweb

Databases are collections of tabulated information stored in a way such that it is easy to access a single record by searching, sorting, or other

An Excel spreadsheet is a good example of a basic database table; an Excel workbook with many tables is a database, albiet one that fails the 'easy to access'

In the context of uWeb, we will be talking about Relational Database Management Systems, such as MySQL, PostgreSQL, MSSQL, Oracle, DB2, Berkeley DB, SQLite, and other engines that may be used in the development of websites and web applications. Not all databases are appropriate for use with websites; Microsoft Access is a great example of a database engine you would not want to use in a web application.

RDBMS

Relational Database Management Systems are different because they not only manage information stored in tables like Excel, but they also manage the Relationships between the information in the tables using a set of Keys. You can Join these keys together to form more complete pictures of your information. For instance, let's say that you have a user named Alice Jones, and she logs in to your application using 'ajones'. You keep her name, Alice Jones, in a Users table, and log actions she takes in a Logs table. The query to see what Alice did, displayed with her full name, looks like this:

SELECT Users.fullName, Log.timeStamp, Log.action 
FROM Users,Logs 
WHERE Logs.userID = 'ajones' 
AND Logs.userID = Users.userID;

Queries

Queries are the method of accessing information in a database. The query specifies a list of fields to show, the tables from which to get the information, and any limitations that you wish to place upon the information returned, including summarizations.

Important Note: Each RDBMS will have it's own particular query syntax, even though all syntaxes are based upon the ANSI SQL standard.

User Interfaces

Each database may have several User Interface methods, but there is nearly always a command line or method with which you can work with queries directly. Please see the individual RDBMS articles listed below.