AVG returns the average value from a group of values. The group is determined by the FROM clause that follows and may represent all records or a subset. 

Basic Syntax

In its most basic form, the AVG returns the grand total for a field value in all records returned by the rest of the query. 

AVG( <field-name> ) FROM <from-clause>

Examples

The following field example returns the average donation for Donor:

(SELECT AVG(D.Donation_Amount) 
  FROM Donations D 
  WHERE D.Donor_ID = Donors.Donor_ID) AS [First Donation]

Resources

• MSDN — AVG Function