Mysql/PDO-设置变量 [英] Mysql / PDO - Setting Variable
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问题描述
我在尝试设置变量然后在select语句中使用它时遇到了麻烦.我不断收到一般错误",无法弄清楚我在做什么错.任何输入将不胜感激.我正在尝试使用带有命名参数的子查询来设置变量.
I'm having trouble trying to set a variable then use it in a select statement. I keep getting a "general error" and can't figure out what I'm doing wrong. Any input would be appreciate. I'm trying to set a variable using subqueries with named parameters.
$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();
推荐答案
如果出于某些原因要使用MySQL用户变量,则不需要多查询支持.只要您打开会话(连接),它们(用户变量)就会存在.因此,您可以执行以下操作
If you want to use MySQL user variables, for some reason, you don't need multi-queries support. They (user variables) live as long as you session (connection) is open. Therefore you can do something like this
$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);
示例输出:
array(1) {
[0]=>
array(1) {
["@available"]=>
string(6) "100.00"
}
}
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