presto-main/src/main/java/io/prestosql/sql/planner/SymbolsExtractor.java/SymbolsExtractor/extractNames
class SymbolsExtractor:    public static Set<QualifiedName> extractNames(Expression expression, Set<NodeRef<Expression>> columnReferences)
    {
        ImmutableSet.Builder<QualifiedName> builder = ImmutableSet.builder();
        new QualifiedNameBuilderVisitor(columnReferences).process(expression, builder);
        return builder.build();
    }