Definition
Grouping and Aggregation (Relational Algebra)
The grouping and aggregation operation, denoted by
, is an operator that first partitions tuples of a relation into groups and then computes a single or multiple summary value for each group using an aggregate function. This process involves two main steps:
- Grouping: Tuples that have the same values for all attributes in a specified grouping list are placed into the same group.
- Aggregation: An aggregate function (like
SUM,COUNT,AVG,MIN,MAX) is applied to an attribute of the tuples within each group, producing a single value per group.where:
is the list of attributes to group by is the aggregate function to be applied to each group. This also defines the new attribute for the aggregate value in the result schema (e.g., ) is the input relation The resulting relation consists of the grouping attributes in
and the new attribute(s) generated by the aggregate function(s) in .