Aggregate operations cannot be nested. The following aggregate is not valid and returns an error:
AVG(MAXIMUM (Salary))
Although direct nesting of aggregates is not supported, nested aggregates can be evaluated using a derived table that contains the aggregates to be nested. For more information, see Teradata Vantage™ - Time Series Tables and Operations, B035-1208.
Also, aggregates can be nested in aggregate window functions. The following statement is valid and includes an aggregate SUM function nested in a RANK window function:
SELECT region ,product ,SUM(amount) ,RANK() OVER (PARTITION BY region ORDER by SUM (amount)) FROM table;