fix bigint unsigned null cloumn scan to err type int64

Author: elonnzhang

fields.go

@@ -128,6 +128,7 @@ var (
 	scanTypeInt64      = reflect.TypeOf(int64(0))
 	scanTypeNullFloat  = reflect.TypeOf(sql.NullFloat64{})
 	scanTypeNullInt    = reflect.TypeOf(sql.NullInt64{})
+	scanTypeNullUInt   = reflect.TypeOf(sql.Null[uint64]{})
 	scanTypeNullTime   = reflect.TypeOf(sql.NullTime{})
 	scanTypeUint8      = reflect.TypeOf(uint8(0))
 	scanTypeUint16     = reflect.TypeOf(uint16(0))
@@ -185,6 +186,9 @@ func (mf *mysqlField) scanType() reflect.Type {
 			}
 			return scanTypeInt64
 		}
+		if mf.flags&flagUnsigned != 0 {
+			return scanTypeNullUInt
+		}
 		return scanTypeNullInt
 
 	case fieldTypeFloat: