ASA SQL User's Guide
  Summarizing, Grouping and Sorting Query Results
    Summarizing query results using aggregate functions

Aggregate functions and data types

Some aggregate functions have meaning only for certain kinds of data. For example, you can use SUM and AVG with numeric columns only.

However, you can use MIN to find the lowest value—the one closest to the beginning of the alphabet—in a character type column:

SELECT MIN(last_lname)
FROM  contact