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
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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