User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.77 Safari/535.7
Currently, the MAL plan of a sql UNION clause is translated using appends.
When the input tables are sorted on the same attribute it makes sense to use a merge-union approach, to maintain sortedness in the result.
The expected impact is large for certain applications. For example, this would make it viable to build sorted dictionaries incrementally: appending deltas and then sorting explicitly is no option with large data. This is one of the few show-stoppers I still see to use MonetDB (more) efficiently for IR.
(hint: I know the same core functionality was used within MonetDB/XQuery)
Jul2012-SP1 has been released.
No test needed for feature request