planner: reverse the OFFSET when outer join's inner side is unique

pingcap · Oct 8, 2024 · e0187f8 · e0187f8
1 parent f31b091
commit e0187f8
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Showing 2 changed files with 54 additions and 7 deletions.
diff --git a/pkg/expression/schema.go b/pkg/expression/schema.go
@@ -129,21 +129,47 @@ func (s *Schema) RetrieveColumn(col *Column) *Column {
 }
 
 // IsUniqueKey checks if this column is a unique key.
-func (s *Schema) IsUniqueKey(col *Column) bool {
+func (s *Schema) IsUniqueKey(cols ...*Column) bool {
 	for _, key := range s.Keys {
-		if len(key) == 1 && key[0].EqualColumn(col) {
-			return true
+		if len(key) > len(cols) {
+			continue
 		}
+		allFound := true
+		for _, keyCols := range key {
+			for _, col := range cols {
+				if !keyCols.EqualColumn(col) {
+					allFound = false
+					break
+				}
+			}
+		}
+		if !allFound {
+			continue
+		}
+		return true
 	}
 	return false
 }
 
 // IsUnique checks if this column is a unique key which may contain duplicate nulls .
-func (s *Schema) IsUnique(col *Column) bool {
+func (s *Schema) IsUnique(cols ...*Column) bool {
 	for _, key := range s.UniqueKeys {
-		if len(key) == 1 && key[0].EqualColumn(col) {
-			return true
+		if len(key) > len(cols) {
+			continue
 		}
+		allFound := true
+		for _, keyCols := range key {
+			for _, col := range cols {
+				if !keyCols.EqualColumn(col) {
+					allFound = false
+					break
+				}
+			}
+		}
+		if !allFound {
+			continue
+		}
+		return true
 	}
 	return false
 }

diff --git a/pkg/planner/core/operator/logicalop/logical_join.go b/pkg/planner/core/operator/logicalop/logical_join.go
@@ -1076,9 +1076,30 @@ func (p *LogicalJoin) pushDownTopNToChild(topN *LogicalTopN, idx int, opt *optim
 			}
 		}
 	}
+	count, offset := topN.Count+topN.Offset, uint64(0)
+	if p.JoinType == LeftOuterJoin {
+		innerChild := p.Children()[1]
+		innerJoinKey := make([]*expression.Column, 0, len(p.EqualConditions))
+		for _, eqCond := range p.EqualConditions {
+			innerJoinKey = append(innerJoinKey, eqCond.GetArgs()[1].(*expression.Column))
+		}
+		if innerChild.Schema().IsUniqueKey(innerJoinKey...) || innerChild.Schema().IsUnique(innerJoinKey...) {
+			count, offset = topN.Count, topN.Offset
+		}
+	} else if p.JoinType == RightOuterJoin {
+		innerChild := p.Children()[0]
+		innerJoinKey := make([]*expression.Column, 0, len(p.EqualConditions))
+		for _, eqCond := range p.EqualConditions {
+			innerJoinKey = append(innerJoinKey, eqCond.GetArgs()[0].(*expression.Column))
+		}
+		if innerChild.Schema().IsUniqueKey(innerJoinKey...) || innerChild.Schema().IsUnique(innerJoinKey...) {
+			count, offset = topN.Count, topN.Offset
+		}
+	}
 
 	newTopN := LogicalTopN{
-		Count:            topN.Count + topN.Offset,
+		Count:            count,
+		Offset:           offset,
 		ByItems:          make([]*util.ByItems, len(topN.ByItems)),
 		PreferLimitToCop: topN.PreferLimitToCop,
 	}.Init(topN.SCtx(), topN.QueryBlockOffset())