private long evaluateNotNullExpr(Statistics parentStats, AnnotateStatsProcCtx aspCtx, ExprNodeGenericFuncDesc pred,
        long currNumRows) {
      long noOfNulls = getMaxNulls(parentStats, aspCtx, pred);
      long parentCardinality = currNumRows;
      long newPredCardinality = parentCardinality;

      if (parentCardinality > noOfNulls) {
        newPredCardinality = parentCardinality - noOfNulls;
      } else {
        LOG.error("Invalid column stats: No of nulls > cardinality");
      }

      return newPredCardinality;
    }
removes all values which are outside of the scope of the column
ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java