Cardinality in Power BI refers to the relationship between two tables in a data model. Specifically, it describes how many unique values from one table match the values in another table.
There are four types of cardinality in Power BI:
One-to-one (1:1) cardinality: This means that for every value in one table, there is exactly one corresponding value in the other table. One-to-one relationships are often used when the tables being joined have the same primary key.
One-to-many (1:*) cardinality: This means that for each value in one table, there can be multiple corresponding values in another table. One-to-many relationships are the most common type of relationship in Power BI.
Many-to-one (*:1): A many-to-one relationship means, the column in a given table can have more than one instance of a value, and the other related table has only one instance of a value.
Many-to-many (*:*) cardinality: This means that for each value in one table, there can be many corresponding values in another table, and vice versa. A many-to-many relationship requires a bridge table to connect the two tables.
It’s important to understand cardinality when building a data model in Power BI. It determines how tables can be linked and how data can be queried. Setting the correct cardinality ensures that the data is accurate and that queries run efficiently.
For more details refer – Cardinality of Relationship in Power BI