code: func (col *Column) EvalDuration(ctx sessionctx.Context, row chunk.Row) (types.Duration, bool, error) {
  	if row.IsNull(col.Index) {
  		return types.Duration{}, true, nil
  	}
  	duration := row.GetDuration(col.Index, col.RetType.Decimal)
  	return duration, false, nil
  }
docs: // EvalDuration returns Duration representation of Column.