The error message displayed for the first scenario is now also displayed when the COUNT(DISTINCT <field>) expression is present.

Verified in Aqua Data Studio Aqua Data Studio 14.0.0-rc-13 Build #: 33892 on Ubuntu 12.04( Mongo DB 2.4.3)

Still  problem if count( distinct valuation) change on just distinct valuation or distinct for 2 or more fields 

 SELECT distinct valuation, sum(distinct valuation)  FROM baseaball

--  distinct valuation           sum(distinct valuation)

------------------------------------  ----------------------------------

--                            1                                 (null)                                               

go

 SELECT sum(distinct valuation), distinct valuation  FROM baseaball

--NoViableAltException

go

 SELECT distinct valuation, distinct city  FROM baseaball

--NoViableAltException

go

I think there is a misunderstanding regarding the way the DISTINCT clause is supported in our MongoSQL. These last three scenarios don't comply with the MongoSQL specification for the DISTINCT clause. The proper syntax is:

SELECT [FLATTEN | FLATTEN_ARRAY | JSON] DISTINCT <field> FROM <collection_name>

i.e. the DISTINCT keyword is a clause of the SELECT statement, not an attribute of a projection field. Also, according to our specification, only one projection field can occur when the DISTINCT keyword is present.

However, there was no error message for the first scenario. I've fixed this for the next Mongo JDBC release.

Another syntax related to the DISTINCT keyword is the following one (supported only for the COUNT() aggregate function):

SELECT COUNT(DISTINCT <field>) FROM <collection_name>

Jonathan, please mention it on the Query Reference wiki page.

refresh
http://www.aquaclusters.com/app/home/project/public/aquadatastudio/wikibook/MongoDB/page/Query-Reference/Query-Reference#distinct

and let me know if my addition is okay

Yes, the updated documentation for the DISTINCT clause looks good now. Thank you.

Verified in Aqua Data Studio Aqua Data Studio 14.0.0-rc-20 Build #: 33993 on Ubuntu 12.04( Mongo DB 2.4.3)