What is a relational database?
A relational database is a structured collection of information that is related to a particular subject or purpose, such as an inventory database or a human resources database. You use databases to manage information. Information, such as product name, cost, and on-hand inventory, is stored in a database. Within the database, you organize the data into storage containers called tables. Tables are made up of columns and rows. Columns represent individual fields in a table. Rows represent records of data in a table. You can think of database tables as grids, as in the following example: Each field in the table contains one piece of information. In an employee table, for example, one column contains the employee name, another contains the employee phone number, and the address, city, state, zip, and salary are all stored in their own columns. Each record represents one set of related information. For example, an employee table might store information about one employee per row. The number
Any bit of data in the table above could be the same for more than one product. This would make it difficult to specify and retrieve information on a particular product in the database. Therefore, relational databases are designed to provide each row in every table with a unique identifier called a primary key. The primary key might be a column or set of columns in the table that contains unique data for each row. If there is no such identifier defined, you can add a column to hold a unique numerical identifier for the row. In the example below, we have added the ProductID column as the primary key column.
A relational database can be simplified as being a database which contains several tables linked by primary fields in one table to foreign candidate fields in another and no fields other than the primaries are duplicated. However, your very first lesson in databases should have been to explain exactly what a database is, i.e. made up of tables, which in turn are split into records which are split into fields which you format into specific data types and further format those data types and that each element of a database has two views, design and datasheet/printpreview, everything has to be named.
A relational database consists of a collection of tables that store particular sets of data. The invention of this database system has standardized the way that data is stored and processed. The concept of a relational database derives from the principles of relational algebra, realized as a whole by the father of relational databases, E. F. Codd. Most of the database systems in use today are based on the relational system. The history of the relational database began with Codd’s 1970 paper, A Relational Model of Data for Large Shared Data Banks. This theory established that data should be independent of any hardware or storage system and provided for automatic navigation between the data elements. In practice, this meant that data should be stored in tables and that relationships would exist between the different data sets, or tables. The relation is the primary unit of storage in a relational database, which is a two-dimensional table. A relational database can contain one or more of
