This feature has been in Pinot since 2016
The query language for Pinot (PQL) currently only supports selection, aggregation & group byoperations on columns, and moreover, do not support nested operations. There are a growing number of use-cases of Pinot that require some sort of transformation on the column values, before and/or after performing selection, aggregation & group by. One very common example is when we would want to aggregate metrics over different granularity of times, without needing to pre-aggregate records on the individual granularity outside of Pinot. Another example would be when we would want to aggregate on function (say difference) of multiple columns.