@Override
  public void evaluateGroupBatch(VectorizedRowBatch batch) {
    // No input expression for COUNT(*).
    // evaluateInputExpr(batch);

    // Count all rows.
    count += batch.size;
  }
This class evaluates count(*) for a PTF group.

Count all rows of the group.  No input column/expression.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/ptf/VectorPTFEvaluatorCountStar.java