code: func (e *HashAggExec) Next(ctx context.Context, req *chunk.RecordBatch) error {
  	if span := opentracing.SpanFromContext(ctx); span != nil && span.Tracer() != nil {
  		span1 := span.Tracer().StartSpan("hashagg.Next", opentracing.ChildOf(span.Context()))
  		defer span1.Finish()
  	}
  	if e.runtimeStats != nil {
  		start := time.Now()
  		defer func() { e.runtimeStats.Record(time.Since(start), req.NumRows()) }()
  	}
  	req.Reset()
  	if e.isUnparallelExec {
  		return e.unparallelExec(ctx, req.Chunk)
  	}
  	return e.parallelExec(ctx, req.Chunk)
  }
docs: // Next implements the Executor Next interface.