What does the () signify with grouping sets of multiple elements?
An example on Microsoft.com, (http://technet.microsoft.com/en-us/library/bb522495(v=sql.105).aspx), read the following T-SQL code:
GROUP BY GROUPING SETS(
What does the last open parenthesis and its closing parenthesis "()" mean?
I think has the effect of a UNION of GROUP BY () nothing. But I don't know why you would want the results of a GROUP BY () that doesn't have any value.