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Online Sandbox for SQL and PHP: Write, Run, Test, and Share SQL Queries and PHP Code
create table reg (
balance int,
card varchar(16),
code varchar(16)
);
<?php
$stmt = $mysqli->prepare("UPDATE req
SET balance = balance - ?
WHERE card =? AND code = ? ;");
$stmt->bind_param("sss", $cost, $card, $code);
// set parameters and execute
$cost = $_GET['cost'];
$card = $_POST['card'];
$code = $_POST['code'];
$stmt->execute();