In PostgreSQL 12.1 Documentation chapter 4.2.7. Aggregate Expressions it says
The syntax of an aggregate expression is one of the following: ... aggregate_name (DISTINCT expression [ , ... ] [ order_by_clause ] ) [ FILTER ( WHERE filter_clause ) ] ... I believe this is incorrect in the case where the DISTINCT is on a comma-separated list of expressions. It would imply that this is legal select count(DISTINCT parent_id , name) from mytable but that is rejected with ERROR: function count(bigint, text) does not exist whereas select count(DISTINCT ( parent_id , name) ) from mytable is accepted. So I think to handle all cases the line in the doc should read aggregate_name (DISTINCT ( expression [ , ... ] ) [ order_by_clause ] ) [ FILTER ( WHERE filter_clause ) ] I don't know how to indicate that those extra parentheses can be omitted if the list has only one expression. Cheers, John Lumby
