@Override public RelNode visit(LogicalCorrelate rel) {
      // this means we are hitting nested subquery so don't
      // need to go further
      return rel;
    }
Returns whether there are any correlating variables in this statement.

@return whether there are any correlating variables
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java