Github user cloud-fan commented on the pull request:
https://github.com/apache/spark/pull/2542#issuecomment-56940392
Nice catch! I think the problem is: for a table(a string, b string), when
we run "select a.b from test a join test b", we have 2 options to resolve
`a.b`. One is "table a, column b", another is "table b, column a.b". Here we
know that column a don't have a sub column b, so "table b, column a.b" is
invalid, the only option is "table a, column b". However, the system didn't
know this and report "ambiguousReferences".
But what if we really have a sub column b for column a? Should we report
"ambiguousReferences"? @marmbrus What do you think?
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