plan: always chose the smaller child as outer for IndexJoin (pingcap#…

…7019)

plan/gen_physical_plans.go

@@ -385,8 +385,8 @@ func (p *LogicalJoin) tryToGetIndexJoin(prop *requiredProp) ([]PhysicalPlan, boo
 			plans = append(plans, join...)
 		}
 	case InnerJoin:
-		lhsCardinality := p.Children()[0].statsInfo().Count()
-		rhsCardinality := p.Children()[1].statsInfo().Count()
+		lhsCardinality := p.Children()[0].StatsInfo().Count()
+		rhsCardinality := p.Children()[1].StatsInfo().Count()
 
 		leftJoins := p.getIndexJoinByOuterIdx(prop, 0)
 		if leftOuter && leftJoins != nil {

plan/plan.go

@@ -38,6 +38,9 @@ type Plan interface {
 	replaceExprColumns(replace map[string]*expression.Column)
 
 	context() sessionctx.Context
+
+	// StatsInfo will return the statsInfo for this plan.
+	StatsInfo() *statsInfo
 }
 
 // taskType is the type of execution task.
@@ -205,9 +208,6 @@ type PhysicalPlan interface {
 	// getChildReqProps gets the required property by child index.
 	getChildReqProps(idx int) *requiredProp
 
-	// StatsInfo will return the statsInfo for this plan.
-	StatsInfo() *statsInfo
-
 	// Get all the children.
 	Children() []PhysicalPlan
 
@@ -270,6 +270,10 @@ func (p *baseLogicalPlan) buildKeyInfo() {
 	}
 }
 
+func (p *DataSource) StatsInfo() *statsInfo {
+	return p.statsAfterSelect
+}
+
 func newBasePlan(ctx sessionctx.Context, tp string) basePlan {
 	ctx.GetSessionVars().PlanID++
 	id := ctx.GetSessionVars().PlanID

plan/stats.go

@@ -59,7 +59,7 @@ func (s *statsInfo) scaleByExpectCnt(expectCnt float64) *statsInfo {
 	return s
 }
 
-func (p *basePhysicalPlan) StatsInfo() *statsInfo {
+func (p *basePlan) StatsInfo() *statsInfo {
 	return p.stats
 }