5.5. Lookups

Since you have a relationship between the Jobs and Customers tables, you don't have to enter customer information on each job record. Nor do you want to store that data in both tables. If you display the customer's name and address information on the Jobs layout, and then update the customer's data, it automatically shows on the Jobs layout. This dynamic updating of related data is the essence of a relational database. However, many times you don't want a piece of information to change; you want FileMaker to remember the way it was at a certain point in time. Lookup fields use relationships to do a one-time "copy and paste" of data from one table to another. Once the looked-up data is in its new table, you can edit it, if necessary, but it doesn't change automatically if the related data changes.

Take a look at the Invoices table, for example. When you create an invoice, you attach it to a job. The job is in turn attached to a customer. When it comes time to mail the invoice, you could easily put the address fields from the Customers table occurrence on the Invoice layout, and see the customer's address. But this method is a bad idea for two reasons: