Fix enum literal default validation to match MySQL behavior

- Add validateEnumLiteralDefault method for stricter enum default validation
- Reject numeric index references ('1', 1) for literal enum defaults
- Allow only exact enum value matches for literal defaults
- Preserve original ErrInvalidType format in enum expression
- Fixes enums_with_default_values test failures

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

sql/columndefault.go

@@ -227,6 +227,12 @@ func (e *ColumnDefaultValue) CheckType(ctx *Context) error {
 		if val == nil && !e.ReturnNil {
 			return ErrIncompatibleDefaultType.New()
 		}
+		
+		// For enum literal defaults, use stricter validation than runtime conversion
+		if enumType, isEnum := e.OutType.(EnumType); isEnum {
+			return e.validateEnumLiteralDefault(enumType, val)
+		}
+		
 		_, inRange, err := e.OutType.Convert(ctx, val)
 		if err != nil {
 			return ErrIncompatibleDefaultType.Wrap(err)
@@ -238,6 +244,32 @@ func (e *ColumnDefaultValue) CheckType(ctx *Context) error {
 	return nil
 }
 
+// validateEnumLiteralDefault validates enum literal defaults more strictly than runtime conversions
+// MySQL doesn't allow numeric index references for literal enum defaults
+func (e *ColumnDefaultValue) validateEnumLiteralDefault(enumType EnumType, val interface{}) error {
+	switch v := val.(type) {
+	case string:
+		// For string values, check if it's a direct enum value match
+		enumValues := enumType.Values()
+		for _, enumVal := range enumValues {
+			if enumVal == v {
+				return nil // Valid enum value
+			}
+		}
+		// String doesn't match any enum value, return appropriate error
+		if v == "" {
+			return ErrIncompatibleDefaultType.New()
+		}
+		return ErrInvalidColumnDefaultValue.New("(unknown)")
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
+		// MySQL doesn't allow numeric enum indices as literal defaults
+		return ErrInvalidColumnDefaultValue.New("(unknown)")
+	default:
+		// Other types not supported for enum defaults
+		return ErrIncompatibleDefaultType.New()
+	}
+}
+
 type UnresolvedColumnDefault struct {
 	ExprString string
 }

sql/expression/enum.go

@@ -80,7 +80,7 @@ func (e *EnumToString) Eval(ctx *sql.Context, row sql.Row) (interface{}, error)
 	case string:
 		str = v
 	default:
-		return nil, sql.ErrInvalidType.New(e.Enum.Type().String())
+		return nil, sql.ErrInvalidType.New(val, types.Text)
 	}
 	return str, nil
 }