选择并更新表，然后在值为零时停止选择

Question

I.e amount to pay more than one client for same type of products is $20,000. Client One $12,000, Client Two $3,000, Client Two $5,000. Which to total is $20,000.

I want when buyer clicks to purchase for a product and they are available,

1. Select and update table until buyer amount to pay gets to zero then stop.
2. Count number of rows of those he should pay and update his row.

I have tried

$qry=mysqli_query($link,"Select sum(selleramount) from sellertable Where buyer product>0");
$asum=$row[0];
($row=mysqli_fetch_array($ry));
foreach ($qry as $row) {
    $balance=$buyeramount-$asum;
    mysqli_query($link,"insert into buyertable (amount,seller_id,) values ('$amount_to_payseller','$sellertopayid')");
    mysqli_query($link,"update sellertable set seller amount='$balance'");
}

I have tried but its not working out. I have the idea but how to go about what I want I don't know.

Answer 1

I dont have your data to test it properly, but the Transaction method may work here. Example!

$qry=mysqli_query($link,"Select sum(selleramount) from sellertable Where buyer product>0");
$asum=$row[0];
$mysqli->begin_transaction(MYSQLI_TRANS_START_READ_ONLY);
($row=mysqli_fetch_array($ry));
foreach ($qry as $row) {
    $balance=$buyeramount-$asum;
    mysqli_query($link,"insert into buyertable (amount,seller_id,) values ('$amount_to_payseller','$sellertopayid')");
    mysqli_query($link,"update sellertable set seller amount='$balance'");
}
$mysqli->commit();
$mysqli->close();