Data Analytics Glossary

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Many-to-one

What is Many-to-one?

Many-to-one relationship is the exact same concept as one-to-many, just depending on from which side of the relationship the observation is made. For example, Children and Biological Mother is a many-to-one relationship, many children(siblings) all have the same and only one biological mother, but a mother can have many biological children.

How does Many-to-one work?

In database context, many-to-one relationship is very common and actually is the exact reason why relationship database structure emerged in the first place: The many-to-one asymmetry in data elements created the need and room to optimize efficiency. When related tables are brought together, and it’s a many-to-one relationship. That “one” will just be repeated across different records of the “many”, creating a data element that can potentially be used for data aggregation. When it’s a one-to-many relationship, the result would be confusing because the relationship does not know which of the “many” to pick from. The solution would be either to bring all matching “many” over which can create duplicate situations, or the “many” matches need to be filtered down to one (by taking the max or min for example).

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