What is aggregate Query in Apex?

Aggregate functions in salesforce include AVG(), COUNT(), MIN(), MAX(), SUM().The functions like  SUM() and MAX() in SOQL allow to roll up and summarize the data in a query. The GROUP BY clause in a SOQL query is to avoid iterating through individual query results and used to specify a group of records instead of processing many individual records.

AVG() – Returns the average value of a numeric field
COUNT() – Returns the number of rows matching the query criteria
MIN() – Returns the minimum value of a field
MAX() – Returns the maximum value of a field
SUM() – Returns the total sum of a numeric field
A query that includes an aggregate function returns its results in an array of AggregateResult objects. AggregateResult is a read-only sObject and is only used for query results. The values in the AggregateResult object can be accessed much like a map calling a “get” method with the name of the column.