SQL standard supports EXCLUDE clause within window frame definition.
We currently have it in sql_yacc.yy. The statement is parsed, but ignored:
The question is - should we implement frame exclusion? It doesn't seem to be supported by anybody:
- PostgreSQL: http://www.postgresql.org/docs/9.5/static/sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS
- Oracle: http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions004.htm#SQLRF06174
- MS SQL server: https://msdn.microsoft.com/en-us/library/ms189461.aspx
- Apache Drill: https://drill.apache.org/docs/sql-window-functions-introduction/
- Amazon Redshift: http://docs.aws.amazon.com/redshift/latest/dg/r_Window_function_synopsis.html
If we decide not to support Frame Exclusion, we should disable it in the parser so that it doesn't confuse anybody.