Aggregate and Analytic Functions
Aggregate functions are SQL functions designed to allow data from multiple rows of a table or a view to be summarized. You can invoke the functions in this category only from PL/SQL expressions.
Analytic functions also summarize data from multiple rows, but they differ from aggregate functions because they can return multiple rows from each group, while aggregate functions return only a single row.
Most of the functions in this section may be used as either aggregate or analytic functions. The analytic portion of the syntax can be readily identified by the OVER keyword, which introduces the analytic clause. (See the upcoming “Analytic Clause” section for details.)