Algorithm problem for generating 1 million coupons on JD.com

1 million coupons are generated on JD.com, and the coupon number prefix is ​​QA (such as QAK001, QA0U767, QAJUT55, random coupon number). What algorithm can be used to generate 1 million unique coupons? Do these 1 million coupon numbers have to be stored in the database or cache?

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1 million coupons are generated on JD.com, and the coupon number prefix is ​​QA (such as QAK001, QA0U767, QAJUT55, random coupon number). What algorithm can be used to generate 1 million unique coupons? Do these 1 million coupon numbers have to be stored in the database or cache?

You can refer to the algorithm Bloom Filter

UUID is recommended.

<code>function guid(){
    if (function_exists('com_create_guid')){
        return com_create_guid();
    }else{
        mt_srand((double)microtime()*10000);//optional for php 4.2.0 and up.
        $charid = strtoupper(md5(uniqid(rand(), true)));
        $hyphen = chr(45);// "-"
        $uuid = chr(123)// "{"
                .substr($charid, 0, 8).$hyphen
                .substr($charid, 8, 4).$hyphen
                .substr($charid,12, 4).$hyphen
                .substr($charid,16, 4).$hyphen
                .substr($charid,20,12)
                .chr(125);// "}"
        return $uuid;
    }
}</code>