ecshop 秒杀并发时库存会被减到小于0的解决办法

begin();//开始一个事物处理开始

$sql = "UPDATE ".$GLOBALS[‘a‘]->table(‘seconds_kill‘)."     SET kill_stock = kill_stock - 1     WHERE sk_id=‘".$sk_id."‘ LIMIT 1" ;
$GLOBALS[‘db‘]->query($sql);

$sql = "SELECT kill_stock ".    " FROM ".$GLOBALS[‘a‘]->table(‘seconds_kill‘).    " WHERE sk_id=‘".$sk_id."‘";
$kucun = $GLOBALS[‘db‘]->getOne($sql);

if($kucun<0){
    rollback();
    show_message(‘很抱歉，您购买的商品库存不足！ ‘, ‘返回‘, ‘‘, ‘error‘);
    die();
}else{
    commit();
}

//开始
function begin(){
    $GLOBALS[‘db‘] -> query("set autocommit=0");//设置自动提交
    $GLOBALS[‘db‘] -> query("begin");//事务开始
}

//提交
function commit(){
    $GLOBALS[‘db‘] -> query("commit");//提交
    $GLOBALS[‘db‘] -> query("set autocommit=1");
}

//回滚
function rollback(){
    $GLOBALS[‘db‘] -> query("rollback");//回滚所做的数据库更改
    $GLOBALS[‘db‘] -> query("set autocommit=1");
}