SQL Language Extension: Improved aggregate handling

Syntax
========


GROUP BY
--------
SELECT ... FROM .... [GROUP BY group_by_list]

group_by_list : group_by_item [, group_by_list];

group_by_item : column_name
| ordinal
| udf
| group_by_function;

group_by_function : numeric_value_function
| string_value_function
| case_expression
;

numeric_value_function : EXTRACT '(' timestamp_part FROM value ')';

string_value_function : SUBSTRING '(' value FROM pos_short_integer ')'
| SUBSTRING '(' value FROM pos_short_integer FOR nonneg_short_integer ')'
|  KW_UPPER '(' value ')' 
;