16.20 - Aggregates and GROUP BY - Teradata Vantage NewSQL Engine

Teradata Vantageā„¢ SQL Functions, Expressions, and Predicates

Teradata Database
Teradata Vantage NewSQL Engine
Programming Reference

If you use an aggregate function in the select list of an SQL statement, then either all other columns occurring in the select list must also be referenced by means of aggregate functions or their column name must appear in a GROUP BY clause. For example, the following statement uses an aggregate function and a column in the select list and references the column name in the GROUP BY clause:

   SELECT COUNT(*), Product_ID
   FROM Sales_Table
   GROUP BY Product_ID;

The reason for this is that aggregates return only one value, while a non-GROUP BY column reference can return any number of values.