Mysql/PDO - 设置变量

Question

我在设置变量时遇到了麻烦,然后在select语句中使用它.我不断得到"一般错误",无法弄清楚我做错了什么.任何输入都会很感激.我正在尝试使用带有命名参数的子查询来设置变量.

$query = $dbh->prepare("Set @available = (SELECT SUM(payments) FROM payments WHERE customer = :customer) - (SELECT SUM(charges) FROM charges WHERE customer = :customer); SELECT @available");
$query->bindParam(":customer", $customer);
$query->execute();

Answer 1

如果您想使用MySQL用户变量,出于某种原因,您不需要多查询支持.只要您的会话(连接)打开,它们(用户变量)就会存在.因此你可以做这样的事情

$customer = 1;

try {
    $db = new PDO('mysql:host=localhost;dbname=dbname;charset=UTF8', 'user', 'password');
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

    $sql = "SET @available = (SELECT SUM(payments) FROM payments WHERE customer = ?) - 
                             (SELECT SUM(charges)  FROM charges  WHERE customer = ?)";
    $query = $db->prepare($sql);
    $query->execute(array($customer, $customer));

    $query = $db->prepare("SELECT @available");
    $query->execute();
    $result = $query->fetchAll(PDO::FETCH_ASSOC);
} catch (PDOException $e) {
    echo "Exeption: " .$e->getMessage();
    $result = false;
}
$query = null;
$db = null;

var_dump($result);

样本输出:

array(1) {
  [0]=>
  array(1) {
    ["@available"]=>
    string(6) "100.00"
  }
}