In Power BI, "cardinality" refers to the uniqueness of data values contained in a column of a table. It is an important concept in database management and data modeling, particularly when defining relationships between tables.
There are three main types of cardinality in Power BI:
- One-to-One (1:1): Each value in the primary key column of one table is unique and matches with a unique value in the foreign key column of another table. This type of relationship is rare.
- One-to-Many (1:*): One value in the primary key column of one table can match with multiple values in the foreign key column of another table. This is the most common type of relationship in databases.
- Many-to-Many (:): Multiple values in the primary key column of one table can match with multiple values in the foreign key column of another table. Power BI supports this type of relationship with some limitations, and it requires careful handling to avoid issues with data duplication and ambiguity.
