presto-main/src/main/java/io/prestosql/sql/analyzer/RelationType.java/RelationType/joinWith
class RelationType:    public RelationType joinWith(RelationType other)
    {
        List<Field> fields = ImmutableList.<Field>builder()
                .addAll(this.allFields)
                .addAll(other.allFields)
                .build();

        return new RelationType(fields);
    }