当它应该是xxx量时，SELECT SUM（）总是返回0

Question

需要帮助SELECT SUM（）...这是我的所有查询，无论什么时候运行结果总是0任何正文看到我的问题似乎无法弄清楚...

$data = $db->query("SELECT SUM(credit_amount) FROM a_creditpurchase");

$creditsbought = 0;
while($row = $data->fetch(PDO::FETCH_ASSOC)) {
    $creditsbought += $row['credit_amount'];
}
echo $creditsbought;

Answer 1

试试这个

$data = $db->query("SELECT SUM(credit_amount) as sum FROM a_creditpurchase");

$creditsbought = 0;
$row = $data->fetch(PDO::FETCH_ASSOC);
$creditsbought = $row['sum'];

echo $creditsbought;

Answer 2

您是否尝试过GROUP(credit_amount)的SQL查询？

$data = $db->query("SELECT SUM(credit_amount) FROM a_creditpurchase GROUP(credit_amount)");

Answer 3

这非常有效，谢谢

$data = $db->query("SELECT SUM(credit_amount) as totalAmount FROM a_creditpurchase");

while($row = $data->fetch(PDO::FETCH_ASSOC)) {
$creditsbought += $row['totalAmount'];
}