This command is alternative for $apply, which does not exist in BSL.
This allow you to create simple grouping
Aggregate as sum(), average() and so on are currently not supported.
How to use:
$groupby=fieldname,fieldname ...
Example:
List of all Measurements in QC order (QC by Measurements)
odata4/QCOrderMeasurement?
$select=PosText,QCDescription,QCInfo
&$filter=DocEntry eq 1408
&$orderby=Sort asc
&$groupby=PosText,QCDescription,QCInfo,Sort