plan: fix mistaken conversion from outer join to inner join (cherry-p…

…ick #7689) (#7899)

executor/join_test.go

@@ -912,3 +912,14 @@ func (s *testSuite) TestMergejoinOrder(c *C) {
 		`2.02`,
 	))
 }
+
+func (s *testSuite) TestEmbeddedOuterJoin(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1, t2")
+	tk.MustExec("create table t1(a int, b int)")
+	tk.MustExec("create table t2(a int, b int)")
+	tk.MustExec("insert into t1 values(1, 1)")
+	tk.MustQuery("select * from (t1 left join t2 on t1.a = t2.a) left join (t2 t3 left join t2 t4 on t3.a = t4.a) on t2.b = 1").
+		Check(testkit.Rows("1 1 <nil> <nil> <nil> <nil> <nil> <nil>"))
+}

plan/predicate_push_down.go

@@ -245,20 +245,12 @@ func simplifyOuterJoin(p *LogicalJoin, predicates []expression.Expression) {
 		innerTable, outerTable = outerTable, innerTable
 	}
 
-	var fullConditions []expression.Expression
-
 	// first simplify embedded outer join.
-	// When trying to simplify an embedded outer join operation in a query,
-	// we must take into account the join condition for the embedding outer join together with the WHERE condition.
 	if innerPlan, ok := innerTable.(*LogicalJoin); ok {
-		fullConditions = concatOnAndWhereConds(p, predicates)
-		simplifyOuterJoin(innerPlan, fullConditions)
+		simplifyOuterJoin(innerPlan, predicates)
 	}
 	if outerPlan, ok := outerTable.(*LogicalJoin); ok {
-		if fullConditions != nil {
-			fullConditions = concatOnAndWhereConds(p, predicates)
-		}
-		simplifyOuterJoin(outerPlan, fullConditions)
+		simplifyOuterJoin(outerPlan, predicates)
 	}
 
 	if p.JoinType == InnerJoin {
@@ -298,20 +290,6 @@ func isNullRejected(ctx sessionctx.Context, schema *expression.Schema, expr expr
 	return false
 }
 
-// concatOnAndWhereConds concatenate ON conditions with WHERE conditions.
-func concatOnAndWhereConds(join *LogicalJoin, predicates []expression.Expression) []expression.Expression {
-	numAllFilters := len(join.EqualConditions) + len(join.LeftConditions) + len(join.RightConditions) + len(join.OtherConditions) + len(predicates)
-	allFilters := make([]expression.Expression, 0, numAllFilters)
-	for _, equalCond := range join.EqualConditions {
-		allFilters = append(allFilters, equalCond)
-	}
-	allFilters = append(allFilters, join.LeftConditions...)
-	allFilters = append(allFilters, join.RightConditions...)
-	allFilters = append(allFilters, join.OtherConditions...)
-	allFilters = append(allFilters, predicates...)
-	return allFilters
-}
-
 // PredicatePushDown implements LogicalPlan PredicatePushDown interface.
 func (p *LogicalProjection) PredicatePushDown(predicates []expression.Expression) (ret []expression.Expression, retPlan LogicalPlan) {
 	var push = make([]expression.Expression, 0, p.Schema().Len())