About the optimizer's choice of sort avoidance

Some SQL statements require that data be ordered, including those with ORDER BY, GROUP BY, and DISTINCT. MIN() and MAX() aggregates also require ordering of data.

Derby can sometimes avoid sorting steps for:

statements with ORDER BY
See Cost-based ORDER BY sort avoidance

Derby can also perform the following optimizations, but they are not based on cost:

sort avoidance for DISTINCT and GROUP BYs
See Non-cost-based sort avoidance (tuple filtering)
statements with a MIN() aggregate
See The MIN() and MAX() optimizations