For example, if you delete an employee from the Employees table, you also delete the benefits records for that employee from the Benefits table. Referential data integrity helps Access to keep your data clean by deleting related records. Important: When you create a one-to-one relationship, decide carefully whether to enforce referential data integrity for the relationship. That way, you never accidentally add the ID of a car that doesn’t actually exist.
For example, make the Car ID field in the Employees table a lookup field that looks for a value in the Car ID index from the Company Cars table. Often, the best way to create this relationship is to have the secondary table look up a value from the first table.
You create one-to-one relationships by linking the index (usually the primary key) in one table and an index in another table which shares the same value. In this case, you’d create three separate tables-Contacts, Employees, and Subcontractors- and then create a one-to-one relationship between the Contacts and Employees tables and a one-to-one relationship between the Contacts and Subcontractors tables. For subcontractors, you want to know their company name, phone number, and bill rate, among other things. For the employees, you want to know their employee number, their extension, and other key information. For example, you might have a contacts table in which some people are employees and other people are subcontractors. You might use one-to-one relationships if you have a table containing a list of items, but the specific information you want to capture about them varies by type. Each employee appears only once in the Employees table, and each car appears only once in the Company Cars table. For example, there might be a one-to-one relationship between employees and the cars they drive.
One-to-one relationships are frequently used to indicate critical relationships so you can get the data you need to run your business.Ī one-to-one relationship is a link between the information in two tables, where each record in each table only appears once. Try it! What is a one-to-one relationship?
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