private void processSubQueryUnionMerge(GenMRProcContext ctx,
      GenMRUnionCtx uCtxTask, UnionOperator union, Stack<Node> stack)
      throws SemanticException {
    // The current plan can be thrown away after being merged with the union
    // plan
    Task<?> uTask = uCtxTask.getUTask();
    ctx.setCurrTask(uTask);
    TableScanOperator topOp = ctx.getCurrTopOp();
    if (topOp != null && !ctx.isSeenOp(uTask, topOp)) {
      GenMapRedUtils.setTaskPlan(ctx.getCurrAliasId(), ctx
          .getCurrTopOp(), uTask, false, ctx);
    }
  }
Union Operator encountered. A map-only query is encountered at the given
position. However, at least one sub-query is a map-reduce job. Copy the
information from the current top operator to the union context.

@param ctx
@param uCtxTask
@param union
@param stack
@throws SemanticException
ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRUnion1.java