PDO 和嵌套获取

问题描述

假设我有这样的事情:

$db=new PDO($dsn);

$statement=$db->query('Select * from foo');

while ($result=$statement->fetch())
{
    //do something with $result
}

我如何在 while 循环中放置另一个查询?即使我创建了一个新的 PDOStatement 对象，它似乎也会覆盖最顶层 PDO 语句的游标.我看到的唯一其他解决方案是 a) 一次获取整个外部循环或 b) 打开 2 个不同的数据库连接.这些似乎都不是一个好主意，还有其他解决方案吗?

How would I put another query inside of that while loop? Even if I make a new PDOStatement object, it seems that that overwrites the cursor for the topmost PDO statement. The only other solution I see is to either a) fetch the entire outer loop at once or b) open 2 different connections to the database. Neither of these seem like a good idea, are there any other solutions?

推荐答案

你应该能够在你的 while 循环中执行任何你想要的其他查询，我想说；像这样:

You should be able to do any other query you want inside your while loop, I'd say ; something like this :

$db=new PDO($dsn);

$statement=$db->query('Select * from foo');

while ($result=$statement->fetch())
{
    $statement2 = $db->query('Select * from bar');
    while ($result2=$statement2->fetch()) {
        // use result2
    }
}

你试过了吗?它应该工作...

Did you try that ? It should work...

尽管如此，如果可以(如果您的数据没问题，我的意思是)，使用 JOIN 仅执行一个查询可能会提高性能:1 个查询而不是多个查询通常更快.

Still, if you can (if it's OK with your data, I mean), using a JOIN to do only one query might be better for performances : 1 query instead of several is generally faster.

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