How to generate unique and non-repeating strings in php

The only non-repeating method for php to generate a string: 1. Encrypt the current timestamp with md5 and intercept the first 6 digits; 2. Use the database bigint to auto-increment the field and convert it to 62 to shorten the length.

## The operating environment of this article: Windows 7 system, PHP version 7.1 , DELL G3 computer

How does PHP generate a 6-digit non-repeating string?

PHP generates a 6-digit non-repeating string (similar to UUID)

We must consider:

1. No duplication.

2. Security.

【 不建议使用啥敏感的数据作为订单生成规则(例如:用户UID,订单自增ORDER_ID等),以为会暴露网站一些敏感信息】

3. Large-scale random codes cannot be used.

why?

First of all, I ask you "Can randomness in a programming language be truly random?", I can tell you without confidence that at least PHP can't do it, so it may lead to the first The principle of "non-repetition" occurs
1. If your order quantity reaches 10 million times, you have to compare 10 million pieces of historical data every time you generate an order code. Generally, when it reaches 5 million, you have to spend time on database optimization (Simple processing: use partitioning and create indexes. However, the practical requirements are high and you may need to operate under the main database. I wonder how painful it is for you. Of course, there are other optimization methods for real-time reading and writing of the database, which will not be introduced here) .

4. Prevent concurrency.

5. Number of control digits.

why？
1. 便于查询检索
2 位数控制到 10-20位即可，当然网上将的是10~15缘由是利于输入,对于输入太长做好用户体验就好(新增复制订单按钮)

6. Try to have business significance (not mandatory, based on the company’s business)

【当你业务比较庞大时候，或者后期有大规模的扩充时，建议考虑下订单的生成意义，根据公司的业务做调整。举个最简单的例子："一个卖化妆品的商城，你需要根据订单来源来(pc/移动)来生成报表，这时候可能需要"】

7. Solution

// 类似生成 UUID ,不依赖外部流水号，完全靠时间戳和随机数生成订单号无法避免冲突，
// 所以必须引入外部的流水号生成机制。或使用数据库，或使用APC之类的缓存。
// 用APC之类的缓存存在一个问题，就是无法持久保持数据，服务器重启或者PHP宿主进程重启都会清空流水号计数器，
// 所以可以采取缓存+数据库结合的模式——如果缓存中有流水号计数器数据则读取并累加计数，如果缓存中没有流水号计数器从数据库中还原计数器。
// 计数器可以每隔一段时间重置一次。既然引入了自增流水号计数器，又会导致文章开头的“德国坦克问题”，
// 所以需要用skip32算法把流水号加密
// （https://github.com/nlenepveu/Skip32）。

// 订单号 = 日期前缀 + 加密流水号

// Skip32 算法加密密钥
const ENCRYPTED_KEY = 'xxxxxxxxxxxx';

// 使用 Wincache 作为流水号计数器缓存
function getOrderSerialNumber() {
    $timestamp = time();
    $datePrefix = date('ymd', $timestamp);
// 如果流水号计数器数据不在缓存中，则尝试从数据库中恢复
    if (false === ($value = wincache_ucache_inc($datePrefix))) {
    wincache_lock($datePrefix);
// 从数据库中获取今日的订单数
    $counter = getNumberOfOrdersTodayFromDatabase($timestamp);
    $value = $counter + 1;
if (!wincache_ucache_add($datePrefix, $value, 60*60*24)) {
    $value = wincache_ucache_inc($datePrefix);
}
    wincache_unlock($datePrefix);
}
    return $datePrefix.str_pad(Skip32::encrypt($datePrefix.ENCRYPTED_KEY, $value), 10, '0', STR_PAD_LEFT);
}

Simple way:

1. The current timestamp is md5 encrypted and the first 6 digits are intercepted

echo substr(md5(microtime(true)), 0, 6);

2. Use the database bigint to increment the field and convert it to 62 to shorten the length

echo gmp_strval(gmp_init('9876543210', 10), 62);

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