What about the result set of compound selects or of natural joins where the origin column is ambiguous? If knowing the original column is so important, what do people do with those cases?
Since this was brought up, I'll answer it as a separate thread.
The short answer is that the person writing the SQL needs to do a bit more work, and explicitly define an extra result column whose value differs for each member of the compound query, so one knows which said member the row came from.
For example:
SELECT 'first' AS member, foo, bar, baz FROM table_one UNION SELECT 'second' AS member, foo, bar, baz FROM table_two
As for natural joins ... by definition a natural join combines columns that have the same name and equal values in every row; because of this, it is known that each returned value returns to both source columns.
-- Darren Duncan
