plan: push a handle into schema if datasource's schema have no col. (#…

…5447) (#5585)

model/model.go

@@ -87,6 +87,9 @@ func (c *ColumnInfo) IsGenerated() bool {
 // for use of execution phase.
 const ExtraHandleID = -1
 
+// ExtraHandleName is the name of ExtraHandle Column.
+var ExtraHandleName = NewCIStr("_rowid")
+
 // TableInfo provides meta data describing a DB table.
 type TableInfo struct {
 	ID      int64  `json:"id"`
@@ -169,6 +172,16 @@ func (t *TableInfo) GetPkColInfo() *ColumnInfo {
 	return nil
 }
 
+// NewExtraHandleColInfo mocks a column info for extra handle column.
+func NewExtraHandleColInfo() *ColumnInfo {
+	colInfo := &ColumnInfo{
+		ID:   ExtraHandleID,
+		Name: ExtraHandleName,
+	}
+	colInfo.Flag = mysql.PriKeyFlag
+	return colInfo
+}
+
 // ColumnIsInIndex checks whether c is included in any indices of t.
 func (t *TableInfo) ColumnIsInIndex(c *ColumnInfo) bool {
 	for _, index := range t.Indices {

plan/column_pruning.go

@@ -18,6 +18,7 @@ import (
 	"github.com/pingcap/tidb/ast"
 	"github.com/pingcap/tidb/context"
 	"github.com/pingcap/tidb/expression"
+	"github.com/pingcap/tidb/model"
 	"github.com/pingcap/tidb/util/types"
 )
 
@@ -167,7 +168,6 @@ func (p *DataSource) PruneColumns(parentUsedCols []*expression.Column) {
 	if p.unionScanSchema != nil {
 		used[handleIdx] = true
 	}
-	firstCol, firstColInfo := p.schema.Columns[0], p.Columns[0]
 	for i := len(used) - 1; i >= 0; i-- {
 		if !used[i] {
 			p.schema.Columns = append(p.schema.Columns[:i], p.schema.Columns[i+1:]...)
@@ -181,8 +181,8 @@ func (p *DataSource) PruneColumns(parentUsedCols []*expression.Column) {
 	// For SQL like `select 1 from t`, tikv's response will be empty if no column is in schema.
 	// So we'll force to push one if schema doesn't have any column.
 	if p.schema.Len() == 0 {
-		p.schema.Append(firstCol)
-		p.Columns = append(p.Columns, firstColInfo)
+		p.Columns = append(p.Columns, model.NewExtraHandleColInfo())
+		p.schema.Append(p.newExtraHandleSchemaCol())
 	}
 }
 

plan/explain_test.go

@@ -260,13 +260,13 @@ func (s *testExplainSuite) TestExplain(c *C) {
 		{
 			"select sum(6 in (select c2 from t2)) from t1",
 			[]string{
-				"TableScan_22   cop table:t1, range:(-inf,+inf), keep order:true 8000",
-				"TableReader_23 HashSemiJoin_20  root data:TableScan_22 8000",
+				"TableScan_11   cop table:t1, range:(-inf,+inf), keep order:false 8000",
+				"TableReader_12 HashSemiJoin_10  root data:TableScan_11 8000",
 				"TableScan_13 Selection_14  cop table:t2, range:(-inf,+inf), keep order:false 10",
 				"Selection_14  TableScan_13 cop eq(6, test.t2.c2) 10",
-				"TableReader_15 HashSemiJoin_20  root data:Selection_14 10",
-				"HashSemiJoin_20 StreamAgg_9 TableReader_23,TableReader_15 root right:TableReader_15, aux 8000",
-				"StreamAgg_9  HashSemiJoin_20 root type:stream, funcs:sum(5_aux_0) 1",
+				"TableReader_15 HashSemiJoin_10  root data:Selection_14 10",
+				"HashSemiJoin_10 HashAgg_8 TableReader_12,TableReader_15 root right:TableReader_15, aux 8000",
+				"HashAgg_8  HashSemiJoin_10 root type:complete, funcs:sum(5_aux_0) 1",
 			},
 		},
 	}

plan/logical_plan_builder.go

@@ -1209,6 +1209,18 @@ func (b *planBuilder) buildTableDual() LogicalPlan {
 	return dual
 }
 
+func (ds *DataSource) newExtraHandleSchemaCol() *expression.Column {
+	return &expression.Column{
+		FromID:   ds.id,
+		DBName:   ds.DBName,
+		TblName:  ds.tableInfo.Name,
+		ColName:  model.ExtraHandleName,
+		RetType:  types.NewFieldType(mysql.TypeLonglong),
+		Position: len(ds.tableInfo.Columns), // set a unique position
+		ID:       model.ExtraHandleID,
+	}
+}
+
 func (b *planBuilder) buildDataSource(tn *ast.TableName) LogicalPlan {
 	handle := sessionctx.GetDomain(b.ctx).StatsHandle()
 	var statisticTable *statistics.Table