expression: fix nil pointer dereference for case expression (#30479) (#…

…31305)

close #30245

expression/builtin_control.go

@@ -16,7 +16,6 @@ package expression
 
 import (
 	"github.com/cznic/mathutil"
-	"github.com/pingcap/tidb/parser/charset"
 	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/types"
@@ -172,7 +171,7 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	l := len(args)
 	// Fill in each 'THEN' clause parameter type.
 	fieldTps := make([]*types.FieldType, 0, (l+1)/2)
-	decimal, flen, isBinaryStr, isBinaryFlag := args[1].GetType().Decimal, 0, false, false
+	decimal, flen, isBinaryFlag := args[1].GetType().Decimal, 0, false
 	for i := 1; i < l; i += 2 {
 		fieldTps = append(fieldTps, args[i].GetType())
 		decimal = mathutil.Max(decimal, args[i].GetType().Decimal)
@@ -181,7 +180,6 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		} else if flen != -1 {
 			flen = mathutil.Max(flen, args[i].GetType().Flen)
 		}
-		isBinaryStr = isBinaryStr || types.IsBinaryStr(args[i].GetType())
 		isBinaryFlag = isBinaryFlag || !types.IsNonBinaryStr(args[i].GetType())
 	}
 	if l%2 == 1 {
@@ -192,7 +190,6 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		} else if flen != -1 {
 			flen = mathutil.Max(flen, args[l-1].GetType().Flen)
 		}
-		isBinaryStr = isBinaryStr || types.IsBinaryStr(args[l-1].GetType())
 		isBinaryFlag = isBinaryFlag || !types.IsNonBinaryStr(args[l-1].GetType())
 	}
 
@@ -207,16 +204,6 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	}
 	fieldTp.Decimal, fieldTp.Flen = decimal, flen
 	types.TryToFixFlenOfDatetime(fieldTp)
-	if fieldTp.EvalType().IsStringKind() && !isBinaryStr {
-		fieldTp.Charset, fieldTp.Collate = DeriveCollationFromExprs(ctx, args...)
-		if fieldTp.Charset == charset.CharsetBin && fieldTp.Collate == charset.CollationBin {
-			// When args are Json and Numerical type(eg. Int), the fieldTp is String.
-			// Both their charset/collation is binary, but the String need a default charset/collation.
-			fieldTp.Charset, fieldTp.Collate = charset.GetDefaultCharsetAndCollate()
-		}
-	} else {
-		fieldTp.Charset, fieldTp.Collate = charset.CharsetBin, charset.CollationBin
-	}
 	if isBinaryFlag {
 		fieldTp.Flag |= mysql.BinaryFlag
 	}
@@ -239,6 +226,7 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	if err != nil {
 		return nil, err
 	}
+	fieldTp.Charset, fieldTp.Collate = bf.tp.Charset, bf.tp.Collate
 	bf.tp = fieldTp
 	if fieldTp.Tp == mysql.TypeEnum || fieldTp.Tp == mysql.TypeSet {
 		switch tp {

expression/collation.go

@@ -242,7 +242,28 @@ func deriveCollation(ctx sessionctx.Context, funcName string, args []Expression,
 		return ec, nil
 	case ast.Case:
 		// FIXME: case function aggregate collation is not correct.
-		return CheckAndDeriveCollationFromExprs(ctx, funcName, retType, args...)
+		// We should only aggregate the `then expression`,
+		// case ... when ... expression will be rewritten to:
+		// args:  eq scalar func(args: value, condition1), result1,
+		//        eq scalar func(args: value, condition2), result2,
+		//        ...
+		//        else clause
+		// Or
+		// args:  condition1, result1,
+		//        condition2, result2,
+		//        ...
+		//        else clause
+		// so, arguments with odd index are the `then expression`.
+		if argTps[1] == types.ETString {
+			fieldArgs := make([]Expression, 0)
+			for i := 1; i < len(args); i += 2 {
+				fieldArgs = append(fieldArgs, args[i])
+			}
+			if len(args)%2 == 1 {
+				fieldArgs = append(fieldArgs, args[len(args)-1])
+			}
+			return CheckAndDeriveCollationFromExprs(ctx, funcName, retType, fieldArgs...)
+		}
 	case ast.Database, ast.User, ast.CurrentUser, ast.Version, ast.CurrentRole, ast.TiDBVersion:
 		chs, coll := charset.GetDefaultCharsetAndCollate()
 		return &ExprCollation{CoercibilitySysconst, UNICODE, chs, coll}, nil

expression/integration_serial_test.go

@@ -1498,6 +1498,18 @@ func TestIssue26662(t *testing.T) {
 		Check(testkit.Rows())
 }
 
+func TestIssue30245(t *testing.T) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustGetErrCode("select case 1 when 1 then 'a' collate utf8mb4_unicode_ci else 'b' collate utf8mb4_general_ci end", mysql.ErrCantAggregate2collations)
+	tk.MustGetErrCode("select case when 1 then 'a' collate utf8mb4_unicode_ci when 2 then 'b' collate utf8mb4_general_ci end", mysql.ErrCantAggregate2collations)
+	tk.MustGetErrCode("select case 1 when 1 then 'a' collate utf8mb4_unicode_ci when 2 then 'b' collate utf8mb4_general_ci else 'b' collate utf8mb4_bin end", mysql.ErrCantAggregate3collations)
+}
+
 func TestCollationForBinaryLiteral(t *testing.T) {
 	store, clean := testkit.CreateMockStore(t)
 	defer clean()

expression/typeinfer_test.go

@@ -840,8 +840,8 @@ func (s *InferTypeSuite) createTestCase4ControlFuncs() []typeInferTestCase {
 		{"case when c_int_d > 1 then c_double_d else c_bchar end", mysql.TypeString, charset.CharsetUTF8MB4, mysql.BinaryFlag, 22, types.UnspecifiedLength},
 		{"case when c_int_d > 2 then c_double_d when c_int_d < 1 then c_decimal else c_double_d end", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, 22, 3},
 		{"case when c_double_d > 2 then c_decimal else 1 end", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 6, 3},
-		{"case when c_time is not null then c_time else c_date end", mysql.TypeDatetime, charset.CharsetUTF8MB4, mysql.BinaryFlag, mysql.MaxDatetimeWidthNoFsp + 3 + 1, 3},
-		{"case when c_time_d is not null then c_time_d else c_date end", mysql.TypeDatetime, charset.CharsetUTF8MB4, mysql.BinaryFlag, mysql.MaxDatetimeWidthNoFsp, 0},
+		{"case when c_time is not null then c_time else c_date end", mysql.TypeDatetime, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxDatetimeWidthNoFsp + 3 + 1, 3},
+		{"case when c_time_d is not null then c_time_d else c_date end", mysql.TypeDatetime, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxDatetimeWidthNoFsp, 0},
 		{"case when null then null else null end", mysql.TypeNull, charset.CharsetBin, mysql.BinaryFlag, 0, types.UnspecifiedLength},
 	}
 }