Working with related tables
Working with related tables
You can create a relational database to allow you to work with data from other tables. A relational database consists of one or more related tables that, when used together, contain the information you need. Each instance of data is stored in only one table at a time but can be accessed and displayed from any related table. You can change any instance of your related data, and the changes appear dynamically in all places. This means that when you change the data in one place, that data is changed wherever it appears, so your data is always up-to-date. Relational databases allow you to work with data in its most current state, set up and manage data efficiently and with flexibility, and save disk space.
To retrieve data from a related table and copy it to the current table, define a lookup. The copied data is now stored in two places, just as if it were copied and pasted into a target field. Looked-up data is current at the time it is copied, but once copied it remains static unless it is looked up again. See Defining and updating lookups.
Concept art showing dynamic and static relationships between two tables
For example, a typical Sales solution may have these tables:
Customers, which stores customer information such as customer names and contact information
Products, which stores information about products and their current prices
LineItems, which stores sales data for each line of an invoice, including the item sold, the quantity, and the price at which it is sold
Invoices, which keeps a record of each invoice; information displayed in each record comes from related records in the Customers and LineItems tables
Because invoices are a mixture of dynamic data and static data, you use related fields and lookups to display your data. Data from related records in Customers is displayed dynamically on the layout in Invoices. Data from Products is displayed in LineItems. The sales price of each line item is static, and is entered from LineItems into a portal on the Invoices layout using a lookup so that totals in the invoice remain unchanged if the prices of the items change in LineItems later.
Invoices database illustrating the example above
Before you begin building a relational database, it’s important to plan it first. See Planning a relational database.
A related table can be in the same file or in an external data source.
Related topics 
Working with the relationships graph
Creating and changing relationships
Adding and selecting table occurrences
Working with related data in portals
Creating a solution