Union is an example of bag (relational) operators that can have more than one input.
In case that schemas from all the input ports are the same, no problem. In case that schemas from all the input ports are not compatible, no problem because we won't process it. In case that schemas from all the input ports are not the same, but compatible, here comes a problem. Example: C = UNION A,B ; Schema(A) = < Int, Chararray > Schema(B) = < Double, Chararray > The output schema will get resolved to < Double, Chararray >. Here is the problem. The Union operator at the moment doesn't support casting in any layer. In this case if we don't cast it, the binary data of Int will get picked up as Double by the downstream operator!! There are a couple solutions for this:- 1) Implement LOUnion and POUnion to support type casting internally 2) Add casting support in LOUnion operator and let the LogicalToPhysical compiler generates LOForeach for it. 3) Explicitly insert LOForEach to do necessary casting between Union and the problematic input. This is analogous to the way we implement implicit casting for expression operators. 4) Don't support "not same but compatible" case at all. I will do (3) because it makes the most sense to me plus incurs the least impact on other modules. Does anyone have problem with it? Pi
