Method alias

core/src/main/java/org/apache/calcite/tools/RelBuilder.java:4427–4427

Assigns an alias to this group key. Used to assign field names in the group operation.

(@Nullable String alias)

     *
     * <p>Used to assign field names in the {@code group} operation. */
    GroupKey alias(@Nullable String alias);

    /** Returns the number of columns in the group key. */
    int groupKeyCount();