Currently, grouping by alias or ordinal is not supported, but sometimes it can be handy.
Some DB vendors support this feature (PostgreSQL, MySQL), but some not (Oracle, MSSQL). In the current Ignite H2-based SQL engine, this feature is not supported. We should decide do we need it in Ignite with calcite-based SQL engine.
This feature can be easily enabled by redefining SqlConformance#isGroupByAlias, SqlConformance#isGroupByOrdinal
And many other.