private static String tableIdentifierString(StageBean<?> stage) {
        if (stage.getField() != null) {
            return tableIdentifierString(stage.getField());
        } else {
            return tableIdentifierString(stage.getIdentifier());
        }
    }
Calculates which reference to use taking "as()" columns into account.
runtime-parent/runtime-join/src/main/java/com/speedment/runtime/join/internal/component/join/AbstractJoinBuilder.java