HP 3000 Manuals

ALLBASE/SQL Performance Guidelines

Using MIN/MAX Functions in Predicates 

An index scan may be used for a query containing a single MIN() or MAX()
function in the select list if an index exists on the column the function
is applied to, and if the function is applied to the first column in the
index.  The index scan is considered for queries with or without
predicates, including MIN() or MAX() on a join column in a nested loop
join, provided the MIN() or MAX() is applied to a column in the outermost
table.

An index scan plan for MIN() or MAX() cannot be considered for queries in
which there is an expression, an ORDER BY or GROUP BY clause, or where
tables are joined using the sort/merge join method.

MPE/iX 5.0 Documentation