06/10/2019
Relational Databases
Access is a relational database management system. Access data is stored in related tables, where data in one table (such as Customers) is related to data in another table (such as Orders). Access maintains the relationships between related tables, making it easy to extract a customer and all the customer’s orders, without losing any data or pulling order records not owned by the customer.
Multiple tables simplify data entry and reporting by decreasing the input of redundant data. By defining two tables for an application that uses customer information, for example, you don’t need to store the customer’s name and address every time the customer purchases an item.
After you’ve created the tables, they need to be related to each other. For example, if you have a Customers table and a Sales table, you can relate the two tables using a common fi eld between them. In this case, Customer Number would be a good field to have in both tables. This will allow you to see sales in the Sales table where the Customer Number matches the Customers table.
The benefit of this model is that you don’t have to repeat key attributes about a customer (like customer name, address, city, state, zip) each time you add a new record to the Sales table. All you need is the customer number. When a customer changes address, for example, the address changes only in one record in the Customers table.
Separating data into multiple tables within a database makes a system easier to maintain because all records of a given type are within the same table. By taking the time to properly segment data into multiple tables, you experience a significant reduction in design and work time. This process is known as normalization.
