private Double computeNotEqualitySelectivity(RexCall call) {
    Double tmpNDV = getMaxNDV(call);
    if (tmpNDV == null) {
      // Could not be computed
      return null;
    }

    if (tmpNDV > 1) {
      return (tmpNDV - 1) / tmpNDV;
    } else {
      return 1.0;
    }
  }
NDV of "f1(x, y, z) != f2(p, q, r)" ->
"(maxNDV(x,y,z,p,q,r) - 1)/maxNDV(x,y,z,p,q,r)".
<p>

@param call
@return
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/stats/FilterSelectivityEstimator.java