private RelNode getCorRel(CorRef corVar) {
    final RelNode r = cm.mapCorToCorRel.get(corVar.corr);
    RelNode ret = r.getInput(0);
    return ret;
  }
Create RelNode tree that produces a list of correlated variables.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java