presto-main/src/main/java/io/prestosql/sql/planner/EffectivePredicateExtractor.java/EffectivePredicateExtractor/visitUnion
class EffectivePredicateExtractor:        @Override
        public Expression visitUnion(UnionNode node, Void context)
        {
            return deriveCommonPredicates(node, source -> node.outputSymbolMap(source).entries());
        }