  This chapter deals with three optional points of a SELECT
statement: the GROUP BY clause, the set functions {AVG, COUNT,
MAX, MIN, SUM, EVERY, ANY, SOME, GROUPING}, and the HAVING
clause. Often these things appear together: the common factor is
summaries, or amalgams, of Columns with groups, rather than with
details. We group together where values are equal. For example,
confronted with the detail list {Smith Smith Smith Jones Jones},
we could summarize it to be: "three Smiths, two Joneses". Such a
summary is known in SQL as a grouped Table.