Cardinality

What Does Cardinality Mean in a Database?

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Radu works as a full-time data engineer. He loves SQL and anything data-related. In his spare time, he likes to put his data to work by building data pipelines. He even trains machine learning models to predict the best time of the day to drink his coffee. He also enjoys helping others and sharing his knowledge on our blog and Stack Overflow.

Cardinality in an SQL database isn’t just a number representing rows in a table. It also has an impact on query performance. Learn how database cardinality works in this article. Cardinality is a term that originates from mathematics – more specifically, from relational algebra. But the term isn’t limited to the mathematical field; it also has implications in the world of databases. In this article, we will do a dive deep into this topic and explain cardinality in SQL databases and how it impacts your queries.

What Is Cardinality in Data Modeling? The Theory and Practice of Database Cardinality

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Leigh van der Veen

Leigh is a former professional musician and software developer, now working full-time as a deep-dive technical writer. With a degree in musicology and post-graduate software development qualifications, she is passionate about SQL, everything database, cloud-based technologies, and infrastructure. She dives deeply into these technologies, learning everything there is to know. When not writing informative content, she spends time out in nature, walking her dogs, and making patchwork quilts.

What is cardinality in data modeling? And how do you implement cardinality in databases? This discussion uses simple, easy-to-follow examples to describe both the theory and modeling of cardinality in ER diagrams. Cardinality is a mathematical term. It translates into the number of elements in a set. In databases, cardinality refers to the relationships between the data in two database tables. Cardinality defines how many instances of one entity are related to instances of another entity.