Should we support DISTINCT for aggregate functions that are computed over a window?
PostgreSQL doesn't support this:
http://www.postgresql.org/docs/9.5/static/sql-expressions.html says "Aggregate window functions, unlike normal aggregate functions, do not allow DISTINCT or ORDER BY to be used within the function argument list"
SQL Server doesn't support it:
(verified with SQL Server 2008 and 2014)
but one can find many requests for them to support this.
Sybase documentation says:
No aggregation functions in the rank query are allowed to specify DISTINCT
Does this mean they don't support it?
Oracle 12.1 gives this error
Apache Drill DOESNT support it: