Software & Apps MS Office One-to-One Relationships One-to-one relationships are an integral part of building a database by Mike Chapple Writer Former Lifewire writer Mike Chapple is an IT professional with more than 10 years' experience cybersecurity and extensive knowledge of SQL and database management. our editorial process Twitter Mike Chapple Updated on April 05, 2020 alexsl / Getty Images MS Office Word Excel Powerpoint Outlook Tweet Share Email One-to-one relationships occur when there is exactly one record in the first table that corresponds to one record in the related table. For example, U.S. citizens have a Social Security number. Only one number allocates per person. The tables below feature a one-to-one relationship because each row in the first table is directly related to another row in the second table. Employee Number First Name Last Name 123 Rick Rossin 456 Rob Halford 789 Eddie Henson 567 Amy Bond So the number of rows in the employee names table matches the number of rows in the employee positions table. Employee number Position Phone Ext. 123 Associate 6542 456 Manager 3251 789 Associate 3269 567 Manager 9852 Another type of database model is the one-to-many relationship. Using the bottom table you can see that Rob Halford is a manager, so his relationship to the position is one-to-one because at this company a person only has one position. But the manager position includes two people, Amy Bond and Rob Halford, which is a one-to-many relationship. One position, many people. More from Lifewire Introduction to Database Relationships Database Relationships The Fundamentals of SQL Creating Database Relationships in Access Databases for Beginners Guide to Database Relationships in Microsoft Access 2013 One-to-Many Relationships in a Database Entity-Relationship Diagram What Are Database Dependencies? What Is a Database? Creating Relationships Between Tables in Microsoft Access 2010 How Referential Integrity Ensures Database Consistency Multivalued Dependency in Database Design Basic Keys That Make Database Management Easy Definition of Database Relation What Is a Database Management System (DBMS)?