Several solutions to generate unique ids in php

After checking online, there are many methods

1. md5(time() . mt_rand(1,1000000));

This method has a certain probability of duplication

2. PHP built-in function uniqid()

The uniqid() function generates a unique ID based on the current time in microseconds.

There is a sentence in the w3school reference manual Words: "Because it is based on system time, the ID generated by this function is not optimal. To generate an absolutely unique ID, please use the md5() function."

The following method returns similar results: 5DDB650F-4389-F4A9-A100-501EF1348872

function uuid() {
    if (function_exists ( 'com_create_guid' )) {
        return com_create_guid ();
    } else {
        mt_srand ( ( double ) microtime () * 10000 ); //optional for php 4.2.0 and up.随便数播种，4.2.0以后不需要了。
        $charid = strtoupper ( md5 ( uniqid ( rand (), true ) ) ); //根据当前时间（微秒计）生成唯一id.
        $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;
    }
}

com_create_guid() is PHP’s own method of generating a unique ID. It seems to have disappeared after PHP5.
3. The official uniqid() reference manual has methods provided by users, and the results are similar: {E2DFFFB3-571E-6CFC-4B5C-9FEDAAF2EFD7}

public function create_guid($namespace = '') {     
    static $guid = '';
    $uid = uniqid("", true);
    $data = $namespace;
    $data .= $_SERVER['REQUEST_TIME'];
    $data .= $_SERVER['HTTP_USER_AGENT'];
    $data .= $_SERVER['LOCAL_ADDR'];
    $data .= $_SERVER['LOCAL_PORT'];
    $data .= $_SERVER['REMOTE_ADDR'];
    $data .= $_SERVER['REMOTE_PORT'];
    $hash = strtoupper(hash('ripemd128', $uid . $guid . md5($data)));
    $guid = '{' .   
            substr($hash,  0,  8) . 
            '-' .
            substr($hash,  8,  4) .
            '-' .
            substr($hash, 12,  4) .
            '-' .
            substr($hash, 16,  4) .
            '-' .
            substr($hash, 20, 12) .
            '}';
    return $guid;
  }

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