Github user fhueske commented on a diff in the pull request: https://github.com/apache/flink/pull/311#discussion_r23070484 --- Diff: flink-compiler/src/main/java/org/apache/flink/compiler/dag/BinaryUnionNode.java --- @@ -266,4 +268,44 @@ public void computeOutputEstimates(DataStatistics statistics) { this.estimatedOutputSize = in1.estimatedOutputSize > 0 && in2.estimatedOutputSize > 0 ? in1.estimatedOutputSize + in2.estimatedOutputSize : -1; } + + public static class UnionSemanticProperties implements SemanticProperties { + + @Override + public FieldSet getTargetFields(int input, int sourceField) { + if (input != 0 && input != 1) { + throw new IndexOutOfBoundsException(); --- End diff -- That's an internal exception. If something fails here, there is something wrong with the optimizer. Nothing a user can solve. Could make that clear though...
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