当我尝试使用PHP变量查询时，PDO查询返回bool（false）

I'm trying to make a query with a PHP variable ($key) from $_POST form data, and I used bindParam to bind the parameter to the variable.

    foreach ($_POST as $key => $value) {
      if (isset($value) && is_numeric($value)) {
        $sql = "SELECT productPrice FROM products WHERE productName=:productName";
        $stmt = $conn->prepare($sql);
        $stmt->bindParam(':productName', $key, PDO::PARAM_STR);
        $stmt->execute();

        $result = $stmt->fetch(PDO::FETCH_ASSOC);
        var_dump($result);
    }

This returns 'bool(false)' on my page, and I'm not sure why it's doing that. I made sure the $key variable accurately matches the data on the SQL table that I'm querying for.

You are assigning your $key to $value

foreach ($_POST as $key => $value) {

And after this you are still using $key instead of $value in this line

$stmt->bindParam(':productName', $key, PDO::PARAM_STR);

Try using this,

$stmt->bindParam(':productName', $value, PDO::PARAM_STR);

I hope it'll help you.