This is an automated cherry-pick of #54681

Signed-off-by: ti-chi-bot <[email protected]>

pkg/executor/index_lookup_merge_join.go

@@ -441,12 +441,16 @@ func (imw *innerMergeWorker) handleTask(ctx context.Context, task *lookUpMergeJo
 		}
 	}
 	task.memTracker.Consume(int64(cap(task.outerOrderIdx)))
+<<<<<<< HEAD:pkg/executor/index_lookup_merge_join.go
 	failpoint.Inject("IndexMergeJoinMockOOM", func(val failpoint.Value) {
 		if val.(bool) {
 			panic("OOM test index merge join doesn't hang here.")
 		}
 	})
 	// needOuterSort means the outer side property items can't guarantee the order of join keys.
+=======
+	// NeedOuterSort means the outer side property items can't guarantee the order of join keys.
+>>>>>>> 628b7ed6739 (planner: deprecate index lookup merge join. (#54681)):pkg/executor/join/index_lookup_merge_join.go
 	// Because the necessary condition of merge join is both outer and inner keep order of join keys.
 	// In this case, we need sort the outer side.
 	if imw.outerMergeCtx.needOuterSort {

pkg/executor/index_lookup_merge_join_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+<<<<<<< HEAD:pkg/executor/index_lookup_merge_join_test.go
 func TestIndexLookupMergeJoinHang(t *testing.T) {
 	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/executor/IndexMergeJoinMockOOM", `return(true)`))
 	defer func() {
@@ -41,6 +42,8 @@ func TestIndexLookupMergeJoinHang(t *testing.T) {
 	require.Equal(t, "OOM test index merge join doesn't hang here.", err.Error())
 }
 
+=======
+>>>>>>> 628b7ed6739 (planner: deprecate index lookup merge join. (#54681)):pkg/executor/join/index_lookup_merge_join_test.go
 func TestIssue18068(t *testing.T) {
 	require.NoError(t, failpoint.Enable("github.com/pingcap/tidb/pkg/executor/testIssue18068", `return(true)`))
 	defer func() {
@@ -64,3 +67,18 @@ func TestIssue18068(t *testing.T) {
 	tk.MustExec("select  /*+ inl_merge_join(s)*/ 1 from t join s on t.a = s.a limit 1")
 	tk.MustExec("select  /*+ inl_merge_join(s)*/ 1 from t join s on t.a = s.a limit 1")
 }
+
+func TestIssue54064(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists A, B")
+	tk.MustExec("create table A\n(id int primary key nonclustered auto_increment,\nx varchar(32) not null,\ny char(5) not null,\nz varchar(25) not null,\nkey idx_sub_tsk(z,x,y)\n)")
+	tk.MustExec("create table B\n( y char(5) not null,\nz varchar(25) not null,\nx varchar(32) not null,\nprimary key(z, x, y) nonclustered\n)\n")
+	tk.MustExec("insert into A (y, z, x) values\n('CN000', '123', 'RW '),\n('CN000', '456', '123');")
+	tk.MustExec("insert into B values\n('CN000', '123', 'RW '),\n('CN000', '456', '123');")
+	tk.MustQuery("select /*+ inl_merge_join(a, b) */\na.*\nfrom a join b on a.y=b.y and a.z=b.z and a.x = b.x\nwhere a.y='CN000' order by 1,2;").Check(
+		testkit.Rows("1 RW  CN000 123", "2 123 CN000 456"))
+	res := tk.MustQuery("explain format='brief' select /*+ inl_merge_join(a, b) */\na.*\nfrom a join b on a.y=b.y and a.z=b.z and a.x = b.x\nwhere a.y='CN000' order by 1,2;")
+	require.NotRegexp(t, "IndexMergeJoin_.*", res.Rows()[0][0])
+}

pkg/executor/partition_table_test.go

@@ -1182,49 +1182,49 @@ func TestPartitionTableWithDifferentJoin(t *testing.T) {
 	// tk.MustHavePlan(queryHash, "IndexMergeJoin")
 	// tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 	tk.MustQuery(queryHash)
-	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|Optimizer Hint /*+ INL_MERGE_JOIN(trange, trange2) */ is inapplicable"))
+	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|The INDEX MERGE JOIN hint is deprecated for usage, try other hints."))
 
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, trange2) */ * from trange, trange2 where trange.a=trange2.a and trange.a > %v and trange2.a > %v;", x1, x2)
 	// queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v and tregular4.a > %v;", x1, x2)
 	// tk.MustHavePlan(queryHash, "IndexMergeJoin")
 	// tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 	tk.MustQuery(queryHash)
-	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|Optimizer Hint /*+ INL_MERGE_JOIN(trange, trange2) */ is inapplicable"))
+	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|The INDEX MERGE JOIN hint is deprecated for usage, try other hints."))
 
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, trange2) */ * from trange, trange2 where trange.a=trange2.a and trange.a > %v and trange.b > %v;", x1, x2)
 	// queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v and tregular2.b > %v;", x1, x2)
 	// tk.MustHavePlan(queryHash, "IndexMergeJoin")
 	// tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 	tk.MustQuery(queryHash)
-	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|Optimizer Hint /*+ INL_MERGE_JOIN(trange, trange2) */ is inapplicable"))
+	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|The INDEX MERGE JOIN hint is deprecated for usage, try other hints."))
 
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, trange2) */ * from trange, trange2 where trange.a=trange2.a and trange.a > %v and trange2.b > %v;", x1, x2)
 	// queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v and tregular4.b > %v;", x1, x2)
 	// tk.MustHavePlan(queryHash, "IndexMergeJoin")
 	// tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 	tk.MustQuery(queryHash)
-	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|Optimizer Hint /*+ INL_MERGE_JOIN(trange, trange2) */ is inapplicable"))
+	tk.MustQuery("show warnings").Check(testkit.RowsWithSep("|", "Warning|1815|The INDEX MERGE JOIN hint is deprecated for usage, try other hints."))
 
 	// group 6
 	// index_merge_join range partition and regualr table
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, tregular4) */ * from trange, tregular4 where trange.a=tregular4.a and trange.a > %v;", x1)
 	queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v;", x1)
-	tk.MustHavePlan(queryHash, "IndexMergeJoin")
+	tk.MustNotHavePlan(queryHash, "IndexMergeJoin")
 	tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, tregular4) */ * from trange, tregular4 where trange.a=tregular4.a and trange.a > %v and tregular4.a > %v;", x1, x2)
 	queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v and tregular4.a > %v;", x1, x2)
-	tk.MustHavePlan(queryHash, "IndexMergeJoin")
+	tk.MustNotHavePlan(queryHash, "IndexMergeJoin")
 	tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, tregular4) */ * from trange, tregular4 where trange.a=tregular4.a and trange.a > %v and trange.b > %v;", x1, x2)
 	queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v and tregular2.b > %v;", x1, x2)
-	tk.MustHavePlan(queryHash, "IndexMergeJoin")
+	tk.MustNotHavePlan(queryHash, "IndexMergeJoin")
 	tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 
 	queryHash = fmt.Sprintf("select /*+ inl_merge_join(trange, tregular4) */ * from trange, tregular4 where trange.a=tregular4.a and trange.a > %v and tregular4.b > %v;", x1, x2)
 	queryRegular = fmt.Sprintf("select /*+ inl_merge_join(tregular2, tregular4) */ * from tregular2, tregular4 where tregular2.a=tregular4.a and tregular2.a > %v and tregular4.b > %v;", x1, x2)
-	tk.MustHavePlan(queryHash, "IndexMergeJoin")
+	tk.MustNotHavePlan(queryHash, "IndexMergeJoin")
 	tk.MustQuery(queryHash).Sort().Check(tk.MustQuery(queryRegular).Sort().Rows())
 
 	// group 7

pkg/executor/test/jointest/hashjoin/hash_join_test.go

@@ -377,11 +377,6 @@ func TestExplainAnalyzeJoin(t *testing.T) {
 	require.Equal(t, 7, len(rows))
 	require.Regexp(t, "HashJoin.*", rows[0][0])
 	require.Regexp(t, "time:.*, loops:.*, build_hash_table:{total:.*, fetch:.*, build:.*}, probe:{concurrency:5, total:.*, max:.*, probe:.*, fetch and wait:.*}", rows[0][5])
-	// Test for index merge join.
-	rows = tk.MustQuery("explain analyze select /*+ INL_MERGE_JOIN(t1, t2) */ * from t1,t2 where t1.a=t2.a;").Rows()
-	require.Len(t, rows, 9)
-	require.Regexp(t, "IndexMergeJoin_.*", rows[0][0])
-	require.Regexp(t, fmt.Sprintf(".*Concurrency:%v.*", tk.Session().GetSessionVars().IndexLookupJoinConcurrency()), rows[0][5])
 
 	// TestExplainAnalyzeIndexHashJoin
 	// Issue 43597

pkg/executor/test/jointest/join_test.go

@@ -136,10 +136,10 @@ func TestJoin2(t *testing.T) {
 	// The physical plans of the two sql are tested at physical_plan_test.go
 	tk.MustQuery("select /*+ INL_JOIN(t, t1) */ * from t join t1 on t.a=t1.a").Check(testkit.Rows("1 1 1 2", "1 1 1 3", "1 1 1 4", "3 3 3 4"))
 	tk.MustQuery("select /*+ INL_HASH_JOIN(t, t1) */ * from t join t1 on t.a=t1.a").Sort().Check(testkit.Rows("1 1 1 2", "1 1 1 3", "1 1 1 4", "3 3 3 4"))
-	tk.MustQuery("select /*+ INL_MERGE_JOIN(t, t1) */ * from t join t1 on t.a=t1.a").Check(testkit.Rows("1 1 1 2", "1 1 1 3", "1 1 1 4", "3 3 3 4"))
+	tk.MustQuery("select /*+ INL_MERGE_JOIN(t, t1) */ * from t join t1 on t.a=t1.a").Check(testkit.Rows("1 1 1 4", "1 1 1 3", "1 1 1 2", "3 3 3 4"))
 	tk.MustQuery("select /*+ INL_JOIN(t) */ * from t1 join t on t.a=t1.a and t.a < t1.b").Check(testkit.Rows("1 2 1 1", "1 3 1 1", "1 4 1 1", "3 4 3 3"))
 	tk.MustQuery("select /*+ INL_HASH_JOIN(t) */ * from t1 join t on t.a=t1.a and t.a < t1.b").Sort().Check(testkit.Rows("1 2 1 1", "1 3 1 1", "1 4 1 1", "3 4 3 3"))
-	tk.MustQuery("select /*+ INL_MERGE_JOIN(t) */ * from t1 join t on t.a=t1.a and t.a < t1.b").Check(testkit.Rows("1 2 1 1", "1 3 1 1", "1 4 1 1", "3 4 3 3"))
+	tk.MustQuery("select /*+ INL_MERGE_JOIN(t) */ * from t1 join t on t.a=t1.a and t.a < t1.b").Check(testkit.Rows("1 4 1 1", "1 3 1 1", "1 2 1 1", "3 4 3 3"))
 	// Test single index reader.
 	tk.MustQuery("select /*+ INL_JOIN(t, t1) */ t1.b from t1 join t on t.b=t1.b").Check(testkit.Rows("2", "3"))
 	tk.MustQuery("select /*+ INL_HASH_JOIN(t, t1) */ t1.b from t1 join t on t.b=t1.b").Sort().Check(testkit.Rows("2", "3"))

pkg/planner/core/casetest/physicalplantest/physical_plan_test.go

@@ -1114,8 +1114,9 @@ func TestIndexJoinHint(t *testing.T) {
 
 	var input []string
 	var output []struct {
-		SQL  string
-		Plan string
+		SQL   string
+		Plan  string
+		Warns []string
 	}
 
 	is := domain.GetDomain(tk.Session()).InfoSchema()
@@ -1124,6 +1125,16 @@ func TestIndexJoinHint(t *testing.T) {
 
 	planSuiteData := GetPlanSuiteData()
 	planSuiteData.LoadTestCases(t, &input, &output)
+	filterWarnings := func(originalWarnings []contextutil.SQLWarn) []contextutil.SQLWarn {
+		warnings := make([]contextutil.SQLWarn, 0, 4)
+		for _, warning := range originalWarnings {
+			// filter out warning about skyline pruning
+			if !strings.Contains(warning.Err.Error(), "remain after pruning paths for") {
+				warnings = append(warnings, warning)
+			}
+		}
+		return warnings
+	}
 	for i, tt := range input {
 		comment := fmt.Sprintf("case:%v sql: %s", i, tt)
 		stmt, err := p.ParseOneStmt(tt, "", "")
@@ -1133,7 +1144,9 @@ func TestIndexJoinHint(t *testing.T) {
 		testdata.OnRecord(func() {
 			output[i].SQL = tt
 			output[i].Plan = core.ToString(p)
+			output[i].Warns = testdata.ConvertSQLWarnToStrings(filterWarnings(tk.Session().GetSessionVars().StmtCtx.GetWarnings()))
 		})
+		tk.Session().GetSessionVars().StmtCtx.TruncateWarnings(0)
 		require.Equal(t, output[i].Plan, core.ToString(p), comment)
 	}
 }

pkg/planner/core/casetest/physicalplantest/testdata/plan_suite_out.json

@@ -2543,23 +2543,34 @@
     "Cases": [
       {
         "SQL": "select /*+ INL_JOIN(t1) */ * from t1 join t2 on t1.a = t2.a;",
-        "Plan": "IndexJoin{IndexLookUp(Index(t1.idx_a)[[NULL,NULL]]->Sel([not(isnull(test.t1.a))]), Table(t1))->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t2.a,test.t1.a)"
+        "Plan": "IndexJoin{IndexLookUp(Index(t1.idx_a)[[NULL,NULL]]->Sel([not(isnull(test.t1.a))]), Table(t1))->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t2.a,test.t1.a)",
+        "Warns": null
       },
       {
         "SQL": "select /*+ INL_HASH_JOIN(t1) */ * from t1 join t2 on t1.a = t2.a;",
-        "Plan": "IndexHashJoin{IndexLookUp(Index(t1.idx_a)[[NULL,NULL]]->Sel([not(isnull(test.t1.a))]), Table(t1))->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t2.a,test.t1.a)"
+        "Plan": "IndexHashJoin{IndexLookUp(Index(t1.idx_a)[[NULL,NULL]]->Sel([not(isnull(test.t1.a))]), Table(t1))->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t2.a,test.t1.a)",
+        "Warns": null
       },
       {
         "SQL": "select /*+ INL_MERGE_JOIN(t1) */ * from t1 join t2 on t1.a = t2.a;",
-        "Plan": "IndexMergeJoin{IndexLookUp(Index(t1.idx_a)[[NULL,NULL]]->Sel([not(isnull(test.t1.a))]), Table(t1))->Projection->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t2.a,test.t1.a)"
+        "Plan": "LeftHashJoin{TableReader(Table(t1)->Sel([not(isnull(test.t1.a))]))->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t1.a,test.t2.a)",
+        "Warns": [
+          "[planner:1815]The INDEX MERGE JOIN hint is deprecated for usage, try other hints."
+        ]
       },
       {
         "SQL": "select /*+ inl_merge_join(t2) */ t1.a, t2.a from t t1 left join t t2 use index(g_2) on t1.g=t2.g",
-        "Plan": "IndexMergeJoin{IndexReader(Index(t.g_2)[[NULL,+inf]])->IndexReader(Index(t.g_2)[[NULL,NULL]]->Sel([not(isnull(test.t.g))]))}(test.t.g,test.t.g)"
+        "Plan": "MergeLeftOuterJoin{IndexReader(Index(t.g_2)[[NULL,+inf]])->IndexReader(Index(t.g_2)[[-inf,+inf]])}(test.t.g,test.t.g)",
+        "Warns": [
+          "[planner:1815]The INDEX MERGE JOIN hint is deprecated for usage, try other hints."
+        ]
       },
       {
         "SQL": "select /*+inl_merge_join(t2)*/ t1.a, t2.a from t t1 left join t t2 use index(g_2) on t1.g=t2.g order by t1.a",
-        "Plan": "IndexMergeJoin{IndexReader(Index(t.g_2)[[NULL,+inf]])->IndexReader(Index(t.g_2)[[NULL,NULL]]->Sel([not(isnull(test.t.g))]))}(test.t.g,test.t.g)->Sort"
+        "Plan": "IndexHashJoin{TableReader(Table(t))->IndexReader(Index(t.g_2)[[NULL,NULL]]->Sel([not(isnull(test.t.g))]))}(test.t.g,test.t.g)",
+        "Warns": [
+          "[planner:1815]The INDEX MERGE JOIN hint is deprecated for usage, try other hints."
+        ]
       }
     ]
   },
@@ -2686,8 +2697,8 @@
       },
       {
         "SQL": "select /*+ INL_MERGE_JOIN(t1) */ t1.b, t2.b from t1 inner join t2 on t1.a = t2.a;",
-        "Plan": "IndexMergeJoin{IndexLookUp(Index(t1.idx_a)[[NULL,NULL]]->Sel([not(isnull(test.t1.a))]), Table(t1))->Projection->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t2.a,test.t1.a)",
-        "Hints": "inl_merge_join(@`sel_1` `test`.`t1`), use_index(@`sel_1` `test`.`t1` `idx_a`), order_index(@`sel_1` `test`.`t1` `idx_a`), use_index(@`sel_1` `test`.`t2` )"
+        "Plan": "LeftHashJoin{TableReader(Table(t1)->Sel([not(isnull(test.t1.a))]))->TableReader(Table(t2)->Sel([not(isnull(test.t2.a))]))}(test.t1.a,test.t2.a)",
+        "Hints": "hash_join(@`sel_1` `test`.`t1`), use_index(@`sel_1` `test`.`t1` ), use_index(@`sel_1` `test`.`t2` )"
       },
       {
         "SQL": "select /*+ MERGE_JOIN(t1) */ t1.b, t2.b from t1 inner join t2 on t1.a = t2.a;",

pkg/util/hint/hint.go

@@ -55,7 +55,7 @@ const (
 	HintINLJ = "inl_join"
 	// HintINLHJ is hint enforce index nested loop hash join.
 	HintINLHJ = "inl_hash_join"
-	// HintINLMJ is hint enforce index nested loop merge join.
+	// Deprecated: HintINLMJ is hint enforce index nested loop merge join.
 	HintINLMJ = "inl_merge_join"
 	// HintNoIndexJoin is the hint to enforce the query not to use index join.
 	HintNoIndexJoin = "no_index_join"
@@ -708,7 +708,10 @@ func ParsePlanHints(hints []*ast.TableOptimizerHint,
 		case HintINLHJ:
 			inlhjTables = append(inlhjTables, tableNames2HintTableInfo(currentDB, hint.HintName.L, hint.Tables, hintProcessor, currentLevel, warnHandler)...)
 		case HintINLMJ:
-			inlmjTables = append(inlmjTables, tableNames2HintTableInfo(currentDB, hint.HintName.L, hint.Tables, hintProcessor, currentLevel, warnHandler)...)
+			if hint.Tables != nil {
+				warnHandler.SetHintWarning("The INDEX MERGE JOIN hint is deprecated for usage, try other hints.")
+				continue
+			}
 		case TiDBHashJoin, HintHJ:
 			hashJoinTables = append(hashJoinTables, tableNames2HintTableInfo(currentDB, hint.HintName.L, hint.Tables, hintProcessor, currentLevel, warnHandler)...)
 		case HintNoHashJoin:

tests/integrationtest/r/executor/index_lookup_join.result

@@ -90,12 +90,12 @@ select /*+ INL_MERGE_JOIN(t1, t2) */ * from t1, t2;
 a	b	a	b
 show warnings;
 Level	Code	Message
-Warning	1815	Optimizer Hint /*+ INL_MERGE_JOIN(t1, t2) */ is inapplicable without column equal ON condition
+Warning	1815	The INDEX MERGE JOIN hint is deprecated for usage, try other hints.
 select /*+ INL_MERGE_JOIN(t1, t2) */ * from t1 join t2 on t1.a=t2.a;
 a	b	a	b
 show warnings;
 Level	Code	Message
-Warning	1815	Optimizer Hint /*+ INL_MERGE_JOIN(t1, t2) */ is inapplicable
+Warning	1815	The INDEX MERGE JOIN hint is deprecated for usage, try other hints.
 drop table if exists t1, t2;
 create table t1(a bigint, b bigint, index idx_a(a));
 create table t2(a bigint, b bigint);
@@ -123,12 +123,12 @@ select /*+ INL_MERGE_JOIN(t1) */ * from t1 left join t2 on t1.a=t2.a;
 a	b	a	b
 show warnings;
 Level	Code	Message
-Warning	1815	Optimizer Hint /*+ INL_MERGE_JOIN(t1) */ is inapplicable
+Warning	1815	The INDEX MERGE JOIN hint is deprecated for usage, try other hints.
 select /*+ INL_MERGE_JOIN(t2) */ * from t1 right join t2 on t1.a=t2.a;
 a	b	a	b
 show warnings;
 Level	Code	Message
-Warning	1815	Optimizer Hint /*+ INL_MERGE_JOIN(t2) */ is inapplicable
+Warning	1815	The INDEX MERGE JOIN hint is deprecated for usage, try other hints.
 drop table if exists t1, t2;
 create table t1 (a int, key(a));
 create table t2 (a int, key(a));