While I was playing a bit with Spark SQL Joins I suddenly faced an exception like
Exception in thread "main" org.apache.spark.sql.catalyst.errors.package$TreeNodeException: Unresolved attributes: foo.
Followed by the parsed SQL statement etc …
Well, in MySQL the error message would have been
"Unknown column 'foo' in field list"
Aka: You are accessing a column/field foo where this field does not exist.
I was already a bit too close to the problem in order to see it at once – and I only found descriptions dealing with nested structures etc (which wasn’t the case in my situation). So it took me a couple of minutes to realize what Spark want to tell me.
Maybe this helps someone else, too.