而tp对null的理解就是''
$sql = "insert into tb_test(id, name, age, remark)values(%d, '%s', %d, '%s')"
->execute($sql, array(1, 'wangwu', 20, 'my name\'s wangwu'));
->execute($sql, array(2, 'zhangsan', 21, null));
-------------------------------------------------------------------------------
|id |name |age |remark |
--------------------------------------------------------------------------------
|1 |wangwu |20 |my name's wangwu |
--------------------------------------------------------------------------------
|2 |zhangsan |21 | |
--------------------------------------------------------------------------------

这才是结果吧.
|2 |zhangsan |21 |<null> |


null != ''