public boolean hasAnyCandidates() {
    if (pushdownPreds == null || pushdownPreds.isEmpty()) {
      return false;
    }
    for (List<ExprNodeDesc> exprs : pushdownPreds.values()) {
      if (!exprs.isEmpty()) {
        return true;
      }
    }
    return false;
  }
Returns the list of pushdown expressions for each alias that appear in the
current operator's RowResolver. The exprs in each list can be combined
using conjunction (AND).

@return the map of alias to a list of pushdown predicates
ql/src/java/org/apache/hadoop/hive/ql/ppd/ExprWalkerInfo.java