重用bindParam变量时出现奇怪的PDO行为

I am perplexed by this unexpected behavior from pdo:

我对pdo的这种意外行为感到困惑：

Consider this simple query i have written:

考虑一下我写的这个简单的查询：

    $username = "vidhu";
    $numResults = 10;

    $db_vc = new PDO(DB_ADDRESS, DB_USER, DB_PASS);
    $stmt = $db_vc->prepare("SELECT username, email FROM users WHERE username = :username LIMIT :numResults");
    $stmt->bindParam(':username', $username, PDO::PARAM_STR);
    $stmt->bindParam(':numResults', $numResults, PDO::PARAM_INT);
    $stmt->execute();
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
    print_r($result);

This gives me the expected output:

这给了我预期的输出：

Array ( [0] => Array ( [username] => vidhu [email] => someone@gmail.com) )

Now here is what baffles me. When i copy and paste the query EXACTLY like so

现在这就是让我感到困惑的地方。当我像这样复制并粘贴查询时

    $username = "vidhu";
    $numResults = 10;       
    $db_vc = new PDO(DB_ADDRESS, DB_USER, DB_PASS);
    $stmt = $db_vc->prepare("SELECT username, email FROM users WHERE username = :username LIMIT :numResults");
    $stmt->bindParam(':username', $username, PDO::PARAM_STR);
    $stmt->bindParam(':numResults', $numResults, PDO::PARAM_INT);
    $stmt->execute();
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
    print_r($result);

    echo "<br />";        

    $username = "vidhu";
    $numResults = 10;   
    $db_vc = new PDO(DB_ADDRESS, DB_USER, DB_PASS);
    $stmt = $db_vc->prepare("SELECT username, email FROM users WHERE username = :username LIMIT :numResults");
    $stmt->bindParam(':username', $username, PDO::PARAM_STR);
    $stmt->bindParam(':numResults', $numResults, PDO::PARAM_INT);
    $stmt->execute();
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);
    print_r($result);

I expect the output also to be duplicated right? so like:

我希望输出也是重复的吗？所以喜欢：

Array ( [0] => Array ( [username] => vidhu [email] => someone@gmail.com ) )
Array ( [0] => Array ( [username] => vidhu [email] => someone@gmail.com) )

but it doesnt produce that output!. The seond query doesnt return anything it shows up like this:

但它不会产生那个输出！ seond查询不会返回它显示的任何内容，如下所示：

Array ( [0] => Array ( [username] => vidhu [email] => xx.vidhuxx@gmail.com ) ) 
Array ( )

Why is this? Can someone explain?

为什么是这样？谁能解释一下？

Edit

编辑

If i remove the :numResults parameter in both the original and the copy and hardcode 10 in the query it works perfectly!

如果我删除原始和副本中的：numResults参数和查询中的硬编码10它完美地工作！

1 个解决方案

#1

Ok So i think i found out the problem.

好吧我觉得我发现了问题所在。

between the first copy and second copy i added var_dump($numResults). When the page is loaded is shows that the variable has been converted to a string after the first copy of the query is executed. I really don't know why that happens.

在第一个副本和第二个副本之间我添加了var_dump（$ numResults）。加载页面时显示在执行查询的第一个副本后变量已转换为字符串。我真的不知道为什么会这样。

Array ( [0] => Array ( [username] => vidhu [email] => someone@gmail.com ) ) 
string(2) "10" 
Array ( )

So the way i fixed it was instead of using $stmt->bindParam i used $stmt->bindValue Again, i don't know the mechanics or what is going on but it works.

所以我修复它的方式不是使用$ stmt-> bindParam我使用$ stmt-> bindValue再次，我不知道机制或发生了什么，但它的工作原理。

It would be nice if someone could explain why this type of behavior occurs i.e Why the variable is changed from a integer to a string.

如果有人可以解释为什么会发生这种行为，那么为什么变量从整数变为字符串会更好。

#1