One of the most important parts of using a database like Microsoft Access is to understand the different types of relationships. Database relationships are associations between tables. They are created using join statements to retrieve data.
There are three main types of relationships to familiarize yourself with: one-to-one, one-to-many and many-to-many. In this post, we’re going to go into more detail regarding these relations so that you know how they work and what their purpose is.
In a one-to-one relationship, one record in a table is associated with one and only one record in another table. For example, in a school database, each student has a student ID, and the ID is assigned to only one student.
One-to-one relationships are the least common but easiest to visualize. Other examples of a one-to-one relationship are:
- A customer has a single customer ID
- A driver has only one license
- Addresses are related to a single zip code
In a one-to-many relationship, one record in a table can be associated with one or more records in another table. An example of this would be a customer sales database that tracks orders. One customer can have many sales orders.
One-to-many relationships are most common and include the following examples:
- A city can have many zip codes
- A state can have many cities
- A student can be registered to many classes
A many-to-many relationship happens when multiple records in a table are associated with multiple records in another table. For instance, customers can purchase various products, and various products can be purchased by many customers.
It’s important to note that most relational databases do not support many-to-many relationships. To avoid this problem, you can use a third table to break up the many-to-many relationship into two one-to-many relationships.
Many-to-many relationships are flexible. Examples of these relationships are:
- The members in a family can own multiple pets
- A doctor has many patients, and the patients see multiple doctors
- Each class has multiple students, and the students take multiple classes
Relationships are the Cornerstone of Relational Databases
Understanding how database relationships work is an important part of using relational databases. Using relations, you can query the database and get results by combining data from different tables into a single table. But in order for the data to be useful, you must know how the information is related.
To learn more about database relationships, contact the database experts from Arkware. We’ll be happy to give you the tools and resources you need to maximize the use of your database. It’s also important that your database is set up correctly so that your queries, forms and reports are accurate.