collate: latin1_bin has the same collate with utf8mb4_bin,utf8_bin

pkg/planner/core/expression_rewriter.go

@@ -728,13 +728,8 @@ func (er *expressionRewriter) handleCompareSubquery(ctx context.Context, planCtx
 		er.err = err
 		return v, true
 	}
-
-	noDecorrelate := hintFlags&hint.HintFlagNoDecorrelate > 0
-	if noDecorrelate && len(coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())) == 0 {
-		b.ctx.GetSessionVars().StmtCtx.SetHintWarning(
-			"NO_DECORRELATE() is inapplicable because there are no correlated columns.")
-		noDecorrelate = false
-	}
+	corCols := coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())
+	noDecorrelate := isNoDecorrelate(planCtx, corCols, hintFlags)
 
 	// Only (a,b,c) = any (...) and (a,b,c) != all (...) can use row expression.
 	canMultiCol := (!v.All && v.Op == opcode.EQ) || (v.All && v.Op == opcode.NE)
@@ -1039,13 +1034,8 @@ func (er *expressionRewriter) handleExistSubquery(ctx context.Context, planCtx *
 		return v, true
 	}
 	np = er.popExistsSubPlan(planCtx, np)
-
-	noDecorrelate := hintFlags&hint.HintFlagNoDecorrelate > 0
-	if noDecorrelate && len(coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())) == 0 {
-		b.ctx.GetSessionVars().StmtCtx.SetHintWarning(
-			"NO_DECORRELATE() is inapplicable because there are no correlated columns.")
-		noDecorrelate = false
-	}
+	corCols := coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())
+	noDecorrelate := isNoDecorrelate(planCtx, corCols, hintFlags)
 	semiJoinRewrite := hintFlags&hint.HintFlagSemiJoinRewrite > 0
 	if semiJoinRewrite && noDecorrelate {
 		b.ctx.GetSessionVars().StmtCtx.SetHintWarning(
@@ -1212,16 +1202,11 @@ func (er *expressionRewriter) handleInSubquery(ctx context.Context, planCtx *exp
 	// If the leftKey and the rightKey have different collations, don't convert the sub-query to an inner-join
 	// since when converting we will add a distinct-agg upon the right child and this distinct-agg doesn't have the right collation.
 	// To keep it simple, we forbid this converting if they have different collations.
+	// tested by TestCollateSubQuery.
 	lt, rt := lexpr.GetType(er.sctx.GetEvalCtx()), rexpr.GetType(er.sctx.GetEvalCtx())
 	collFlag := collate.CompatibleCollate(lt.GetCollate(), rt.GetCollate())
-
-	noDecorrelate := hintFlags&hint.HintFlagNoDecorrelate > 0
 	corCols := coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())
-	if len(corCols) == 0 && noDecorrelate {
-		planCtx.builder.ctx.GetSessionVars().StmtCtx.SetHintWarning(
-			"NO_DECORRELATE() is inapplicable because there are no correlated columns.")
-		noDecorrelate = false
-	}
+	noDecorrelate := isNoDecorrelate(planCtx, corCols, hintFlags)
 
 	// If it's not the form of `not in (SUBQUERY)`,
 	// and has no correlated column from the current level plan(if the correlated column is from upper level,
@@ -1272,6 +1257,16 @@ func (er *expressionRewriter) handleInSubquery(ctx context.Context, planCtx *exp
 	return v, true
 }
 
+func isNoDecorrelate(planCtx *exprRewriterPlanCtx, corCols []*expression.CorrelatedColumn, hintFlags uint64) bool {
+	noDecorrelate := hintFlags&hint.HintFlagNoDecorrelate > 0
+	if noDecorrelate && len(corCols) == 0 {
+		planCtx.builder.ctx.GetSessionVars().StmtCtx.SetHintWarning(
+			"NO_DECORRELATE() is inapplicable because there are no correlated columns.")
+		noDecorrelate = false
+	}
+	return noDecorrelate
+}
+
 func (er *expressionRewriter) handleScalarSubquery(ctx context.Context, planCtx *exprRewriterPlanCtx, v *ast.SubqueryExpr) (ast.Node, bool) {
 	intest.AssertNotNil(planCtx)
 	ci := planCtx.builder.prepareCTECheckForSubQuery()
@@ -1282,13 +1277,8 @@ func (er *expressionRewriter) handleScalarSubquery(ctx context.Context, planCtx
 		return v, true
 	}
 	np = planCtx.builder.buildMaxOneRow(np)
-
-	noDecorrelate := hintFlags&hint.HintFlagNoDecorrelate > 0
-	if noDecorrelate && len(coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())) == 0 {
-		planCtx.builder.ctx.GetSessionVars().StmtCtx.SetHintWarning(
-			"NO_DECORRELATE() is inapplicable because there are no correlated columns.")
-		noDecorrelate = false
-	}
+	correlatedColumn := coreusage.ExtractCorColumnsBySchema4LogicalPlan(np, planCtx.plan.Schema())
+	noDecorrelate := isNoDecorrelate(planCtx, correlatedColumn, hintFlags)
 
 	if planCtx.builder.disableSubQueryPreprocessing || len(coreusage.ExtractCorrelatedCols4LogicalPlan(np)) > 0 || hasCTEConsumerInSubPlan(np) {
 		planCtx.plan = planCtx.builder.buildApplyWithJoinType(planCtx.plan, np, logicalop.LeftOuterJoin, noDecorrelate)

pkg/planner/core/tests/subquery/BUILD.bazel

@@ -0,0 +1,16 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_test")
+
+go_test(
+    name = "subquery_test",
+    timeout = "short",
+    srcs = [
+        "main_test.go",
+        "subquery_test.go",
+    ],
+    flaky = True,
+    deps = [
+        "//pkg/testkit",
+        "//pkg/testkit/testsetup",
+        "@org_uber_go_goleak//:goleak",
+    ],
+)

pkg/planner/core/tests/subquery/main_test.go

@@ -0,0 +1,34 @@
+// Copyright 2025 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package subquery
+
+import (
+	"flag"
+	"testing"
+
+	"github.com/pingcap/tidb/pkg/testkit/testsetup"
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	testsetup.SetupForCommonTest()
+	flag.Parse()
+	opts := []goleak.Option{
+		goleak.IgnoreTopFunction("github.com/golang/glog.(*fileSink).flushDaemon"),
+		goleak.IgnoreTopFunction("github.com/bazelbuild/rules_go/go/tools/bzltestutil.RegisterTimeoutHandler.func1"),
+		goleak.IgnoreTopFunction("github.com/lestrrat-go/httprc.runFetchWorker"),
+	}
+	goleak.VerifyTestMain(m, opts...)
+}

pkg/planner/core/tests/subquery/subquery_test.go

@@ -0,0 +1,48 @@
+// Copyright 2025 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package subquery
+
+import (
+	"testing"
+
+	"github.com/pingcap/tidb/pkg/testkit"
+)
+
+func TestCollateSubQuery(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(id int, col varchar(100), key ix(col)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;")
+	tk.MustExec("create table t1(id varchar(100)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;")
+	samePlan := testkit.Rows(
+		"IndexHashJoin 8000.00 root  inner join, inner:IndexLookUp, outer key:Column#6, inner key:test.t.col, equal cond:eq(Column#6, test.t.col)",
+		"├─HashAgg(Build) 6400.00 root  group by:Column#12, funcs:firstrow(Column#12)->Column#6",
+		"│ └─TableReader 6400.00 root  data:HashAgg",
+		"│   └─HashAgg 6400.00 cop[tikv]  group by:cast(test.t1.id, var_string(5)), ",
+		"│     └─Selection 8000.00 cop[tikv]  not(isnull(cast(test.t1.id, var_string(5))))",
+		"│       └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo",
+		"└─IndexLookUp(Probe) 8000.00 root  ",
+		"  ├─Selection(Build) 8000.00 cop[tikv]  not(isnull(test.t.col))",
+		"  │ └─IndexRangeScan 8008.01 cop[tikv] table:t, index:ix(col) range: decided by [eq(test.t.col, Column#6)], keep order:false, stats:pseudo",
+		"  └─TableRowIDScan(Probe) 8000.00 cop[tikv] table:t keep order:false, stats:pseudo")
+	tk.MustQuery(`explain format="brief" select * from t use index(ix) where col in (select cast(id as char) from t1);`).
+		Check(samePlan)
+	tk.MustExec(`set collation_connection='utf8_bin';`)
+	tk.MustQuery(`explain format="brief" select * from t use index(ix) where col in (select cast(id as char) from t1);`).
+		Check(samePlan)
+	tk.MustExec(`set collation_connection='latin1_bin';`)
+	tk.MustQuery(`explain format="brief" select * from t use index(ix) where col in (select cast(id as char) from t1);`).
+		Check(samePlan)
+}

pkg/util/collate/collate.go

@@ -104,7 +104,7 @@ func NewCollationEnabled() bool {
 func CompatibleCollate(collate1, collate2 string) bool {
 	if (collate1 == "utf8mb4_general_ci" || collate1 == "utf8_general_ci") && (collate2 == "utf8mb4_general_ci" || collate2 == "utf8_general_ci") {
 		return true
-	} else if (collate1 == "utf8mb4_bin" || collate1 == "utf8_bin" || collate1 == "latin1_bin") && (collate2 == "utf8mb4_bin" || collate2 == "utf8_bin") {
+	} else if (collate1 == "utf8mb4_bin" || collate1 == "utf8_bin" || collate1 == "latin1_bin") && (collate2 == "utf8mb4_bin" || collate2 == "utf8_bin" || collate2 == "latin1_bin") {
 		return true
 	} else if (collate1 == "utf8mb4_unicode_ci" || collate1 == "utf8_unicode_ci") && (collate2 == "utf8mb4_unicode_ci" || collate2 == "utf8_unicode_ci") {
 		return true