Hi Mike,
Here is one way
SeedRandom[123];
dataset =
RandomReal[1, {4, 3}] //
MapThread[(Append, {#, {"e", "g", "h", "g"}}] & //
Map[AssociationThread[{"a", "b", "c", "d"} -> #] &, #] & //
Dataset
dataset[Select[#b > 0.3 && MemberQ[{"g", "h"}, #d] &]]