expression: fix wrong result when select with collation (#18665)

expression/builtin.go

@@ -88,7 +88,7 @@ func (b *baseBuiltinFunc) collator() collate.Collator {
 
 func newBaseBuiltinFunc(ctx sessionctx.Context, funcName string, args []Expression) (baseBuiltinFunc, error) {
 	if ctx == nil {
-		panic("ctx should not be nil")
+		return baseBuiltinFunc{}, errors.New("unexpected nil session ctx")
 	}
 	if err := checkIllegalMixCollation(funcName, args); err != nil {
 		return baseBuiltinFunc{}, err
@@ -134,7 +134,7 @@ func newBaseBuiltinFuncWithTp(ctx sessionctx.Context, funcName string, args []Ex
 		panic("unexpected length of args and argTps")
 	}
 	if ctx == nil {
-		panic("ctx should not be nil")
+		return baseBuiltinFunc{}, errors.New("unexpected nil session ctx")
 	}
 
 	for i := range args {
@@ -244,6 +244,26 @@ func newBaseBuiltinFuncWithTp(ctx sessionctx.Context, funcName string, args []Ex
 	return bf, nil
 }
 
+// newBaseBuiltinFuncWithFieldType create BaseBuiltinFunc with FieldType charset and collation.
+// do not check and compute collation.
+func newBaseBuiltinFuncWithFieldType(ctx sessionctx.Context, tp *types.FieldType, args []Expression) (baseBuiltinFunc, error) {
+	if ctx == nil {
+		return baseBuiltinFunc{}, errors.New("unexpected nil session ctx")
+	}
+	bf := baseBuiltinFunc{
+		bufAllocator:           newLocalSliceBuffer(len(args)),
+		childrenVectorizedOnce: new(sync.Once),
+		childrenReversedOnce:   new(sync.Once),
+
+		args: args,
+		ctx:  ctx,
+		tp:   types.NewFieldType(mysql.TypeUnspecified),
+	}
+	bf.SetCharsetAndCollation(tp.Charset, tp.Collate)
+	bf.setCollator(collate.GetCollator(tp.Collate))
+	return bf, nil
+}
+
 func (b *baseBuiltinFunc) getArgs() []Expression {
 	return b.args
 }

expression/distsql_builtin.go

@@ -25,7 +25,6 @@ import (
 	"github.com/pingcap/tidb/sessionctx/stmtctx"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/codec"
-	"github.com/pingcap/tidb/util/collate"
 	"github.com/pingcap/tidb/util/mock"
 	"github.com/pingcap/tipb/go-tipb"
 )
@@ -44,7 +43,7 @@ func PbTypeToFieldType(tp *tipb.FieldType) *types.FieldType {
 
 func getSignatureByPB(ctx sessionctx.Context, sigCode tipb.ScalarFuncSig, tp *tipb.FieldType, args []Expression) (f builtinFunc, e error) {
 	fieldTp := PbTypeToFieldType(tp)
-	base, err := newBaseBuiltinFunc(ctx, fmt.Sprintf("PBSig-%v", sigCode), args)
+	base, err := newBaseBuiltinFuncWithFieldType(ctx, fieldTp, args)
 	if err != nil {
 		return nil, err
 	}
@@ -1132,11 +1131,6 @@ func PBToExpr(expr *tipb.Expr, tps []*types.FieldType, sc *stmtctx.StatementCont
 		return nil, err
 	}
 
-	// recover collation information
-	if collate.NewCollationEnabled() {
-		tp := sf.GetType()
-		sf.SetCharsetAndCollation(tp.Charset, tp.Collate)
-	}
 	return sf, nil
 }
 

expression/integration_test.go

@@ -6719,3 +6719,18 @@ func (s *testIntegrationSerialSuite) TestIssue18702(c *C) {
 	tk.MustExec("ROLLBACK;")
 	tk.MustQuery("SELECT * FROM t FORCE INDEX(idx_bc);").Check(testkit.Rows("1 A 10 1", "2 B 20 1"))
 }
+
+func (s *testIntegrationSerialSuite) TestIssue18662(c *C) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a varchar(10) collate utf8mb4_bin, b varchar(10) collate utf8mb4_general_ci);")
+	tk.MustExec("insert into t (a, b) values ('a', 'A');")
+	tk.MustQuery("select * from t where field('A', a collate utf8mb4_general_ci, b) > 1;").Check(testkit.Rows())
+	tk.MustQuery("select * from t where field('A', a, b collate utf8mb4_general_ci) > 1;").Check(testkit.Rows())
+	tk.MustQuery("select * from t where field('A' collate utf8mb4_general_ci, a, b) > 1;").Check(testkit.Rows())
+	tk.MustQuery("select * from t where field('A', a, b) > 1;").Check(testkit.Rows("a A"))
+}