问题描述
我使用的是PHP，而MySQL使用的是PDO.有时，我需要准备一个在此查询中多次使用一个变量(占位符)的语句.
I'm using PHP, and MySQL with PDO. Sometimes I need to prepare a statement with one variable (placeholder) used more than once in this query.
示例:
SELECT * FROM messages WHERE from_id = :user OR to_id = :user
但是，如果我尝试准备此语句，则会出现错误，因此我需要以如下方式进行操作:
However if I will try to prepare this statement I will have an error so I need to do this in a way like this:
SELECT * FROM messages WHERE from_id = :user1 OR to_id = :user2
要调用此语句，我将需要具有以下数组:
To call this statement I will need to have an array like this:
array('user1'=>$user_id, 'user2'=>$user_id);
对我来说真是太愚蠢了！为什么MySQL(PDO?)不允许我多次使用一个占位符，并迫使我使用需要更多控制权的额外变量?！
It looks so stupid for me! Why MySQL (PDO?) don't allowing me to use one place holder more than once and forcing me to use extra variables which requires more control?!
如果查询相对简单(如我在上面发布的内容)，则可以轻松处理，但是现在我使用单个变量的5(!!!)个用法构建了一个查询.每次添加占位符时，都需要在许多地方检查代码以使其正常.
This can be handled easy if the query is relatively simple (like I posted above), but now I built a query with 5 (!!!) uses of single variable. Each time I add the placeholder I need to check the code in many places to make it OK.
是否有任何设置或调整项可以绕过此设置?
Is there any setting or a tweak to bypass this?
推荐答案
是的，有. 您可以打开仿真模式，并可以多次使用相同的占位符.
Yes, there is. You can turn emulation mode ON and be able to use the same placeholder multiple times.
因此，仅当关闭仿真时，才会观察到所描述的行为.我真的不明白为什么会这样，但这是Wez Furlong(PDO作者)的解释:
So the described behavior is observed only when the emulation is turned OFF. I don't really understand why it is so but here is an explanation from Wez Furlong (the PDO author):
第二个原因是可移植性.一些驱动程序会在内部执行此检查并输出错误.如果您针对不执行此操作的驱动程序进行编码，那么您的代码将不适用于未执行此操作的驱动程序.
The second reason is that of portability. Some drivers would internally perform this check and error out. If you code against the drivers that don’t enforce this, then your code won’t work on those that don’t.
http://paul-m-jones.com/archives/243# comment-740
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