What do you need to help with: the syntax, or the set operations? (Or both?)
Perhaps I'm not experienced enough, but this seems like a requirement that doesn't easily fit into SQL constructs. You could use
EXCEPT, but you'd have to do this before adding the
SOURCE column, because that would cause the otherwise identical "yellow" and "pink" records to differ. So you'd have to process "yellow" records twice (once with the
EXCEPT clause, and once with the
UNION clause).
Another approach could be to create a union including the
SOURCE column, and then use a
GROUP BY to keep only one version of each row.
SOURCE would not be part of the group by, but you'd use
MAX(SOURCE) which would choose "yellow" in rows that have both "pink" and "yellow" versions. Handling three colors this way could be tricky, but you could always use numbers to make the handling easier and translate it to a
string later.
It would be probably good to try several approaches and see which one has the best execution plan.
