One-to-Many Relationship

What Does One-to-Many Relationship Mean?

In relational databases, a one-to-many relationship occurs when a parent record in one table can potentially reference several child records in another table. In a one-to-many relationship, the parent is not required to have child records; therefore, the one-to-many relationship allows zero child records, a single child record or multiple child records. The important thing is that the child cannot have more than one parent record.

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The opposite of a one-to-many relationship is a many-to-many relationship, in which a child record can link back to several parent records.

Techopedia Explains One-to-Many Relationship

Consider a database for recording sales information in a store. There are two tables in this database:

  • The CUSTOMER table: This is used for storing customer master details. Its primary key is the CUST_ID column.
  • The SALES table: This is used for keeping track of individual sales transactions.

The SALES table contains the CUST_ID foreign key, which references the column of the same name in the CUSTOMER table to track the customer to whom the sale was made. A single sales transaction can only apply to one customer, but one customer can have many sales transactions over the course of time. This logic is what is defined by the one-to-many relationship. One, in this example, is one customer to many sales transactions.

The one-to-many relationship is only a principle of database design, which cannot be explicitly defined in the database structure. Instead, it is implicitly created and enforced by the use of relationships between tables, especially the relationship between a primary key and a foreign key.

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Margaret Rouse

Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…