Apache Pinot

The following query compiles with the calcite compiler but the broker request still uses the pql2 compiler which fails:
```select foo from table
where
and case bar when 1,2,3 then 4 when 4,5,6 then 5 when 7 then 6 when 8 then 7 else 17 end = 6
limit 10```

Should `org.apache.pinot.common.request.transform.TransformExpressionTree` use the calcite compiler instead of the pql2 compiler if the endpoint is the "sql" endpoint?

Good point.. we should make that change. <@UDQU92KBK> ^^

Yes, we should make that change within the scope of deprecating PQL. Last time I had looked at it, it didn't seem like a trivial change.

that's the only form of case statement that calcite compiles which doesn't work w pql it seems.

`TransformExpressionTree` is for PQL `BrokerRequest` only. Once we deprecate PQL, we can remove this class

Actually after releasing `0.7`, we can already only compile `PinotQuery` for SQL query and leave `BrokerRequest` empty

We're still on v6 - seems like no matter what it uses the pql compiler in BrokerRequestHandler but only for the filter.