Cardinality is a database design concept that refers to the relationship between database tables and columns. It is generally used when describing the design and structure of a relational database. In a Relational Database Management System (RDBMS), cardinality refers to the number of distinct values that can be held in a column or set of columns. It has two distinct types of cardinality: high-cardinality and low-cardinality.
High-cardinality columns are those with a large number of distinct values and low-cardinality columns are those with fewer distinct values. High-cardinality columns are generally used to identify and distinguish among multiple records and are often used as the primary key of the relation.
Low-cardinality columns are used to store data that is either repetitive or used for computations. For example, a date column would have a low cardinality since the same value could appear multiple times.
SQL is the language used to query a relational database. It is used to create and manipulate databases, build queries, and process data from databases. In SQL, cardinality generally refers to the set of values stored in a column or the set of distinct combinations of values in two or more columns. It’s important to understand cardinality in SQL in order to create optimized queries and ensure accurate, efficient data retrievals.
When designing a database, cardinality should be considered. High-cardinality columns should be chosen as keys in order to design efficient databases that can be queried quickly and accurately. Low-cardinality columns should also be considered and used for computations and data analysis.
Overall, cardinality is an essential concept in database design and SQL to provide a database with good structure and performance.