PDO和嵌套提取 [英] PDO and nested fetching

问题描述

假设我有这样的：

  $ db = new PDO（$ dsn）; 
 
 $ statement = $ db-> query（'Select * from foo'）; 
 
 while（$ result = $ statement-> fetch（））
 {
 //使用$ result执行操作
} 
  

如何将另一个查询放在while循环中？即使我创建了一个新的PDOStatement对象，它似乎覆盖了最上面的PDO语句的游标。我看到的唯一的其他解决方案是a）一次获取整个外部循环或b）打开2个不同的连接到数据库。

解决方案

你应该能够做任何其他查询想在你的while循环，我会说;像这样：

  $ db = new PDO（$ dsn）; 
 
 $ statement = $ db-> query（'Select * from foo'）; 
 
 while（$ result = $ statement-> fetch（））
 {
 $ statement2 = $ db-> query（'Select * from bar'）; 
 while（$ result2 = $ statement2-> fetch（））{
 //使用result2 
} 
} 
  pre> 
 
 
您尝试过吗？它应该工作... 
 
 
 
 
 
仍然，如果你可以（如果你的数据没关系，我的意思），使用JOIN只有一个查询可能更好的性能：1查询，而不是几个通常更快。
 
Let's say I have something like this:
$db=new PDO($dsn);

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

while ($result=$statement->fetch())
{
    //do something with $result
}
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?
解决方案
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
    }
}
Did you try that ? It should work...



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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