code: func (col *CorrelatedColumn) EvalDuration(ctx sessionctx.Context, row chunk.Row) (types.Duration, bool, error) {
  	if col.Data.IsNull() {
  		return types.Duration{}, true, nil
  	}
  	return col.Data.GetMysqlDuration(), false, nil
  }
docs: // EvalDuration returns Duration representation of CorrelatedColumn.