Write a SOQL query to get the sum, average, minimum, and maximum Opportunity Amount grouped by StageName.

Group Opportunities by StageName and apply all four aggregate functions.

SELECT StageName, SUM(Amount) total, AVG(Amount) average, MIN(Amount) smallest, MAX(Amount) largest
FROM Opportunity
GROUP BY StageName

Each row is an AggregateResult; read values with ar.get('total') and so on.