sql/analyzer/optimization_rules.go: moveJoinConditionsToFilter: Fix s…

…mall inaccuracy where computed topJoin could be wrong.

This could result in the optimization pass adding the same Filter node to
multiple places in the join tree.

sql/analyzer/optimization_rules.go

@@ -106,7 +106,8 @@ func moveJoinConditionsToFilter(ctx *sql.Context, a *Analyzer, n sql.Node, scope
 		}
 
 		if filtersMoved == 0 {
-			return n, nil
+			topJoin = n
+			return topJoin, nil
 		}
 
 		if len(condFilters) > 0 {

sql/analyzer/optimization_rules_test.go

@@ -255,6 +255,45 @@ func TestMoveJoinConditionsToFilter(t *testing.T) {
 	)
 
 	assertNodesEqualWithDiff(t, expected, result)
+
+	node = plan.NewInnerJoin(
+		plan.NewResolvedTable(t1, nil, nil),
+		plan.NewInnerJoin(
+			plan.NewResolvedTable(t2, nil, nil),
+			plan.NewResolvedTable(t3, nil, nil),
+			expression.JoinAnd(
+				eq(col(0, "t2", "c"), col(0, "t3", "e")),
+				eq(col(0, "t3", "a"), lit(5)),
+			),
+		),
+		expression.JoinAnd(
+			eq(col(0, "t1", "c"), col(0, "t2", "e")),
+		),
+	)
+
+	result, err = rule.Apply(sql.NewEmptyContext(), NewDefault(nil), node, nil)
+	require.NoError(err)
+
+	expected = plan.NewFilter(
+		expression.JoinAnd(
+			eq(col(0, "t3", "a"), lit(5)),
+		),
+		plan.NewInnerJoin(
+			plan.NewResolvedTable(t1, nil, nil),
+			plan.NewInnerJoin(
+				plan.NewResolvedTable(t2, nil, nil),
+				plan.NewResolvedTable(t3, nil, nil),
+				expression.JoinAnd(
+					eq(col(0, "t2", "c"), col(0, "t3", "e")),
+				),
+			),
+			expression.JoinAnd(
+				eq(col(0, "t1", "c"), col(0, "t2", "e")),
+			),
+		),
+	)
+
+	assertNodesEqualWithDiff(t, expected, result)
 }
 
 func TestEvalFilter(t *testing.T) {