【奇怪的问题】mysql无法update字段的默认值是怎么回事？

yycyycyy

简要来说，就是某字段column_a在插入记录时没有赋值，之后就没法更新了。

具体如下：
两列的create table命令如下：
  `column_a` int(18) DEFAULT '100' COMMENT '无法update',
  `column_b` int(18) DEFAULT '0' COMMENT '可以update',

我插入一条数据，column_a没有赋值，column_b=123
insert table_name (column_b) values (123);

然后我发现该问题，想要更新column_a值，结果出错:
update table_name set column_a = 123213 where id = 1;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'column_a = 123213 where id = 1' at line 1

查询该记录column_a = 100, column_b = 123。
不知道什么原因，于是我写入column_b，发现column_b可以正常更新：
update table_name set column_b = 123213 where id = 1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

着实奇怪。。
mysql版本如下：
Server version: 5.1.54-1ubuntu4-log (Ubuntu)
Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license

kider

专门试了试，我这儿是可以的：

1 queries executed, 1 success, 0 errors, 0 warnings

Query: update a set column_a = 123213 where id = 1

1 row(s) affected

Execution Time : 0.021 sec
Transfer Time  : 0 sec
Total Time     : 0.022 sec

与默认值应该没有关系。