Cardinality in DBMS

In Database Management Systems (DBMS), cardinality refers to the number of elements in a set or the number of relationships between entities in a database. There are a few contexts in which cardinality is important:

1. Cardinality of a Table (Rows):
   This refers to the number of rows (or records) in a table. For example, if a table has 100 rows, its cardinality is 100.
2. Cardinality of Relationships (between Tables):
   This is related to how tables in a database relate to each other. Cardinality can define the type of relationship between two tables, and it can be:
   • One-to-One (1:1): A single row in one table is related to a single row in another table.
   • One-to-Many (1:M): A single row in one table is related to multiple rows in another table.
   • Many-to-Many (M:M): Multiple rows in one table are related to multiple rows in another table.
3. Cardinality in Queries (Set Operations):
   In the context of relational queries, cardinality can refer to the number of distinct results that a query returns. For instance, when using SELECT DISTINCT, you can get a sense of the cardinality of the result set.