SOQL - Aggregate Functions and GROUP BY clause in Salesforce explained in 6 minutes 

What are Aggregate Functions in SOQL?
How to use Aggregate Functions in SOQL?
What is GROUP BY clause in SOQL?
How to use GROUP BY clause in SOQL?
The 5 AGGREGATE FUNCTIONS in SOQL are -
1. COUNT - used to find the count of records that will be returned by a query
2. AVG - used to find the average of a field value across all the records that will be returned by a query
3. MIN - used to find the minimum value of a field across all the records that will be returned by a query
4. MAX - used to find the maximum value of a field across all the records that will be returned by a query
5. SUM - used to find the sum of values of a field across all the records that will be returned by a query