Relational Databases
A relational database is a more-complex database that stores data in multiple tables that are interrelated. Usually the tables in a relational database have one-to-many relationships. For example, you might have one table that stores customer orders and another that stores the line items for each order, and each order table would have one or more line items in the order details table. Another example might be a customers table and an orders table. Each customer may place multiple orders.
The following image shows the Orders, Order Details, and Products tables in the Northwind database.
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As you can see, each table has one or more fields that connect it to a neighboring table. This indicates how each table is related to another table. For example, in this image the Orders table has an OrderID field. The Order Details table also has an OrderID field. Each record in the Order Details table has a value in the OrderID field that matches an order in the Orders table. That's how you can determine which order line items in the Order Details table belong to a specific order in the Orders table. You can create relational databases in database applications such as Microsoft Access, Microsoft SQL Server, Oracle, and MySQL.
For more information about databases, see the following resources.