code: func (p *PhysicalTableScan) ToPB(ctx sessionctx.Context) (*tipb.Executor, error) {
  	columns := p.Columns
  	tsExec := &tipb.TableScan{
  		TableId: p.Table.ID,
  		Columns: model.ColumnsToProto(columns, p.Table.PKIsHandle),
  		Desc:    p.Desc,
  	}
  	err := SetPBColumnsDefaultValue(ctx, tsExec.Columns, p.Columns)
  	return &tipb.Executor{Tp: tipb.ExecType_TypeTableScan, TblScan: tsExec}, err
  }
docs: // ToPB implements PhysicalPlan ToPB interface.