  In this note the precise minimum number of key comparisons any dual-pivot
quickselect algorithm (without sampling) needs on average is determined. The
result is in the form of exact as well as asymptotic formul\ae{} of this number
of a comparison-optimal algorithm. It turns out that the main terms of these
asymptotic expansions coincide with the main terms of the corresponding
analysis of the classical quickselect, but still---as this was shown for
Yaroslavskiy quickselect---more comparisons are needed in the dual-pivot
variant. The results are obtained by solving a second order differential
equation for the generating function obtained from a recursive approach.
