• 使用PDO操作数据
• 生成器使用
• 随机暂停缓解数据库压力
• 批量更新数据

<?php
header('Content-Type: text/html; charset=utf-8');

// 定义数据配置信息
$host   = '';
$dbname = '';
$user   = '';
$pass   = '';
$prefix = '';

try {

    // 是否开启更新执行
    define('DEBUG',true);  // true 执行修改SQL  false 反之，
    $testFor = 0;
    $testNum = 3;  // 测试循环次数 如果开启执行 true 更新SQL，测试无效，

    //每次执行多少条数据
    $everyRow = 1000;
    $start = 0;
    $number = 1; // 序号

    //记录日志
    $loger = function($content){
        $file = '/tmp/sql.log';
        $date = date('Y-m-d H:i:s');
        file_put_contents($file, "[{$date}] | {$content}".PHP_EOL, FILE_APPEND | LOCK_EX);
    };

    // 获取当前时间戳，精确到毫秒
    $getCurrentTime = function () {  
        list ($msec, $sec) = explode(" ", microtime());  
        return (float)$msec + (float)$sec;  
    };

    // 连接数据库
$pdo = new PDO ("mysql:host={$host};dbname={$dbname}", $user, $pass);
    $tableName = $prefix.'order_info';

    // 定义获取数据函数
    $querySql = '';
    $selectQuery = function ($pdo, $tableName, $start, $everyRow) {
        global $querySql;
        $querySql = "SELECT order_id,order_sn,buy_from FROM  {$tableName} WHERE buy_from = 0 LIMIT {$start},{$everyRow}";
        $queryStmt = $pdo->prepare($querySql);
        $queryStmt->execute();
        $result = $queryStmt->fetchAll(PDO::FETCH_ASSOC);
        $queryStmt->closeCursor();
        return $result;
    };

    do {

        // 防止开发时死循环
        if (DEBUG) {
            ++$testFor;
            if ($testFor > $testNum) {
                break;
            }
        }

        // 记录开始时间
        $begin = $getCurrentTime();
        if ($result = $selectQuery($pdo, $tableName, $start, $everyRow)) {

            // 定义生成器
            $getGenerator = function ($data) {
                foreach ($data as $key => $value) {
                    yield $key => $value;
                }
            };

            // 遍历生成器，实现拼接执行SQL语句   1 web UU1%,U1%    2 wap UL%,UM%  3 iOS UA%,UUA%  4 Android UB%,UUB%
            $generator = $getGenerator($result);
            $sql = 'UPDATE '.$tableName.'
                    SET buy_from = CASE order_id';
            $fromArray = ['U1'=>1,'UU1'=>1,'UM'=>2,'UL'=>2,'UA'=>3,'UUA'=>3,'UB'=>4,'UUB'=>4];
            $orderIdStr = ''; 
            foreach ($generator as $value) {
                $order_sn = isset($value['order_sn']) ? trim($value['order_sn']) : false;
                if ($order_sn) {
                    $prefixFrom = substr($order_sn, 0, 2); // 截取字符串
                    if($prefixFrom == 'UU'){  // 快速订单处理
                        $prefixFrom = substr($order_sn, 0, 3);
                        $fromBy = isset($fromArray[$prefixFrom]) ? $fromArray[$prefixFrom] : '';
                    }else{
                        $fromBy = isset($fromArray[$prefixFrom]) ? $fromArray[$prefixFrom] : '';
                    }
                    if ($fromBy) {
                        $orderId = $value['order_id'];
                        $orderIdStr .= $orderId.',';
                        $sql .= " WHEN {$orderId} THEN {$fromBy}";
                    }
                }
            }
            //拼接SQL，处理大数据更新
            $orderIdStrWhere = rtrim($orderIdStr, ",");
            $sql .= ' END WHERE order_id IN ('.$orderIdStrWhere.')';

            $count = 0;
            if (!DEBUG) {
                $stmt = $pdo->prepare($sql);
                $stmt->execute();
                $count = $stmt->rowCount();
                $stmt->closeCursor();
            }

            $end = $getCurrentTime();
            $spend = round($end - $begin,5);
            $memory = memory_get_usage();  // 返回的单位是b,/1024得到kb,/(1024*1024)得到mb 1024*1024 = 1048576
            $logContent = '序号:'.$number.' | 查询SQL:'.$querySql.' | 脚本执行时间为:'.$spend.' 秒 | 影响行数:'.$count.' | 消耗内存:'.($memory / 1048576).' mb';
            $loger($logContent); // 记录日志 
            echo $logContent.'<br/>';
        }

        $start += $everyRow; // 分页记录计数
        ++$number; //序号计数
        // 随机暂停 0.2 - 0.99 秒 缓解并发情况下对DB压力
        usleep(rand(200, 999) * 1000);
    } while ($result = $selectQuery($pdo, $tableName, $start, $everyRow));

} catch (PDOException $e) {
die( "Error!: " . $e->getMessage());
}