blocks|key|828762|text|字符需要是随机的吗？或者只是独一无二的？如果它们只需要是唯一的，那么您可以使用时间戳。基于时间的值将确保唯一性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|828763|如果使用另一种方法，则必须根据数据库检查生成的值，直到得到唯一值为止。|828764|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Do the characters need to be random? Or just unique? If they only need to be unique, you could use a timestamp. Basing the value on time will ensure a uniqueness. 

If you go another route, you'll have to check your generated value against the database until you end up with a unique value.

blocks|key|1983522|text|这将为您提供一个随机的8个字符串：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1983523|substr(str_pad(dechex(mt_rand()),+8,+'0',+STR_PAD_LEFT),+-8);|code-block|syntax|javascript|1983524|点击此处：http://www.richardlord.net/blog/php-password-security|offset|length|1983525|或者，如果用户名字段是唯一的，您还可以使用：|1983526|substr(md5('username+value'),+0,+8);|1983527|虽然这是非常不可能的，特别是对于md5，但这两种情况都不能保证字符串是唯一的，所以我可能会这样做：|1983528|//+Handle+user+registration+or+whatever...

function+generatePID($sUsername)+{
++++return+substr(md5($sUsername),+0,+8);
}

$bUnique+=+false;
$iAttempts+=+0;

while+(!$bUnique+&&+$iAttempts+<+10)+{
++++$aCheck+=+$oDB->findByPID(generatePID("username+value"));+//+Query+the+database+for+a+PID+matching+whats+generated
++++if+(!$aCheck)+{+//+If+nothing+is+found,+exit+the+loop
++++++++$bUnique+=+true;
++++}+else+{
++++++++$iAttempts%2B%2B;
++++}
}

//+Save+PID+and+such...|1983529|..。这可能只会产生1个'check‘查询，在唯一的情况下可能会产生2个，并将确保唯一的字符串。|1983530|entityMap|0|LINK|mutability|MUTABLE|url|http://www.richardlord.net/blog/php-password-security^0|0|0|5|1H|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@$I|15|J|16|1|17]]|A|$]]|$1|K|3|L|5|6|7|18|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|1B|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|1C|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

This will give you a random 8 character string:

<pre><code>substr(str_pad(dechex(mt_rand()), 8, '0', STR_PAD_LEFT), -8);
</code></pre>

Found here: <a href="http://www.richardlord.net/blog/php-password-security" rel="nofollow noreferrer">http://www.richardlord.net/blog/php-password-security</a>

Or if the username field is unique you could also use:

<pre><code>substr(md5('username value'), 0, 8);
</code></pre>

Though it's extremely unlikely, particularly for the md5, neither case guarantees a unique string, so I would probably do something like this:

<pre><code>// Handle user registration or whatever...

function generatePID($sUsername) {
 return substr(md5($sUsername), 0, 8);
}

$bUnique = false;
$iAttempts = 0;

while (!$bUnique &amp;&amp; $iAttempts &lt; 10) {
 $aCheck = $oDB-&gt;findByPID(generatePID("username value")); // Query the database for a PID matching whats generated
 if (!$aCheck) { // If nothing is found, exit the loop
 $bUnique = true;
 } else {
 $iAttempts++;
 }
}

// Save PID and such...
</code></pre>

... which would probably only yield 1 'check' query, maybe 2 in unique cases, and would ensure a unique string.

blocks|key|680247|text|为什么不以正确的方式使用UUID(也称为GUID)，它们总是唯一的，不需要检查它们是否是唯一的。它可能有36个字符，但您可以将它们存储为十六进制，这节省了磁盘空间并提高了比标准CHAR数据更快的速度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|680248|你可以在PHP+doc+for+functions+that+do+this上阅读评论。|offset|length|680249|entityMap|0|LINK|mutability|MUTABLE|url|http://us3.php.net/manual/en/function.uniqid.php^0|0|4|Y|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Why not do this the correct way and use UUIDs (aka GUIDs), which are always unique, no need to check if they are or not. It may be 36 chars, but you get the benefit of storing them as HEX which saves disk space and increase speed over standard CHAR data.

You can read the comments on the <a href="http://us3.php.net/manual/en/function.uniqid.php" rel="nofollow noreferrer">PHP doc for functions that do this</a>.

blocks|key|2237055|text|如果您将PID值设置为8个字符，那么您将需要一些东西来生成字符串，并检查它是否还不存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2237056|$alphabet+=+range('A','Z');

//+get+all+the+PIDs+from+the+database
$sql+=+"select+PID+from+mytable";

//+save+those+all+to+an+array
$pid_array+=+results+of+query+saved+to+array

shuffle($alphabet);
$pid_offer+=+array_slice($alphabet,0,8);

while(in_array($pid_offer,+$pid_array)){
++++shuffle($alphabet);
++++$pid_offer+=+array_slice($alphabet,0,8);
}

//+found+uniuqe+$pid_offer...|code-block|syntax|javascript|2237057|竞争条件仍然存在。|2237058|如果字符串不需要是随机的，那么使用ID值，它可能是一个自动递增的整数，并从10000000开始计数。|2237059|然后，只需对该数字中的数字进行简单的A=1、B=2、C=3等替换，即可生成字符串。|2237060|您的里程可能会有所不同。|2237061|--马克|2237062|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

If you're set on 8 characters for the PID value then you'll need something to generate the string and check that it doesn't already exist.

<pre><code>$alphabet = range('A','Z');

// get all the PIDs from the database
$sql = "select PID from mytable";

// save those all to an array
$pid_array = results of query saved to array

shuffle($alphabet);
$pid_offer = array_slice($alphabet,0,8);

while(in_array($pid_offer, $pid_array)){
 shuffle($alphabet);
 $pid_offer = array_slice($alphabet,0,8);
}

// found uniuqe $pid_offer...
</code></pre>

race conditions still exist.

If the string doesn't need to be random, then use the ID value, which is probably an auto-increment integer and start the count for that at 10000000.

Then just do a simple A=1, B=2, C=3 etc replacement on the digits in that number to generate your string.

Your mileage may vary.

--Mark

blocks|key|680269|text|在Mysql中可以这样创建8个字符的唯一字符串|type|unstyled|depth|inlineStyleRanges|entityRanges|data|680270|CAST(MD5(RAND())+as+CHAR(8))|code-block|syntax|javascript|680271|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can create 8 chars unique string in Mysql in such a way

<pre><code>CAST(MD5(RAND()) as CHAR(8))
</code></pre>

blocks|key|680982|text|我的解决方案是在|type|unstyled|depth|inlineStyleRanges|entityRanges|data|680983|中生成随机字符串并检查它是否存在。如果它存在，那么它将生成另一个字符串。|blockquote|680984|680985|680986|这是错误的做法。web服务器将同时运行代码的多个实例，迟早，两个实例将在您的数据库中存储相同的PID。|offset|length|style|CODE|680987|解决这个问题的正确方法是将PID列设置为UNIQUE，并且不需要进行任何预检查。只需运行INSERT查询，并检查结果。|680988|如果结果是1062+(ER_DUP_ENTRY)错误，请生成新的PID并重试。|680989|任何其他数据库错误都应该像平常一样处理。|680990|可能是这样的(未经测试)：|680991|<?php

/*+$link+=+MySQLi+connection+*/

if+(!($stmt+=+mysqli_prepare+('INSERT+`t`+(`ID`,+`Username`,+`PID`)+VALUES+(?,+?,+?)')))+{
++++/*+Prepare+error+*/
}
if+(!mysqli_bind_param+('iss',+$id,+$user,+$pid)+{
++++/*+Bind+error+*/
}

$e+=+0;

for+($i+=+0;+$i+<+10;+$i%2B%2B)+{
++++$pid+=+/*+generate+random+string+*/;
++++if+(mysqli_stmt_execute+($stmt))+
++++++++break;++/*+success+*/
++++$e+=+mysqli_stmt_errno+($stmt);
++++if+($e+!==+1062)
++++++++break;++/*+other+error+*/
}
mysqli_stmt_close+($stmt);

if+($e)+{
++++if+($e+===+1062)+{
++++++++/*+Failed+to+generate+unique+PID+*/
++++}+else+{
++++++++/*+Other+database+error+*/
++++}
}+else+{
++++/*+success+*/
}|code-block|syntax|javascript|680992|entityMap^0|0|0|0|0|1B|3|0|D|3|K|6|18|6|0|5|J|W|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|12|8|@]|9|@]|A|$]]|$1|E|3|-4|5|6|7|13|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|15|8|@$I|16|J|17|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|18|8|@$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1F|8|@$I|1G|J|1H|K|L]|$I|1I|J|1J|K|L]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1K|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1L|8|@]|9|@]|A|$]]|$1|U|3|V|5|W|7|1M|8|@]|9|@]|A|$X|Y]]|$1|Z|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|10|$]]

<blockquote>
 My solution is to generate the random string in PHP and check if it exists. If it exists then it will generate another string.
</blockquote>

This is the wrong way to do it. The web server will run multiple instances of your code concurrently, and sooner or later, two instances will store the same <code>PID</code> in your database.

The correct way to solve this problem is to make the <code>PID</code> column <code>UNIQUE</code>, and don't bother with any pre-checks. Just run the <code>INSERT</code> query, and check the result. 

If the result is a <code>1062 (ER_DUP_ENTRY)</code> error, generate a new <code>PID</code> and try again.

Any other database error should be dealt with like you normally would.

Perhaps something like this (untested):

<pre><code>&lt;?php

/* $link = MySQLi connection */

if (!($stmt = mysqli_prepare ('INSERT `t` (`ID`, `Username`, `PID`) VALUES (?, ?, ?)'))) {
 /* Prepare error */
}
if (!mysqli_bind_param ('iss', $id, $user, $pid) {
 /* Bind error */
}

$e = 0;

for ($i = 0; $i &lt; 10; $i++) {
 $pid = /* generate random string */;
 if (mysqli_stmt_execute ($stmt)) 
 break; /* success */
 $e = mysqli_stmt_errno ($stmt);
 if ($e !== 1062)
 break; /* other error */
}
mysqli_stmt_close ($stmt);

if ($e) {
 if ($e === 1062) {
 /* Failed to generate unique PID */
 } else {
 /* Other database error */
 }
} else {
 /* success */
}
</code></pre>

I'm using PHP and MySQL and
I have a table with 3 fields ((<code>ID</code>, <code>Username</code>, <code>PID</code>)).

I want the <code>PID</code> field to contain strings of 8 unique characters. 

My solution is to generate the random string in PHP and check if it exists. If it exists then it will generate another string.

Is there any better solution that will save processing time, like a MySQL trigger or something like that?

Insert unique strings of 8 random characters

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我使用PHP和MySQL，我有一个包含3个字段((ID，Username，PID))的表。我希望PID字段包含8个唯一字符的字符串。我的解决方案是在PHP中生成随机字符串，并检查它是否存在。如果它存在，那么它将生成另一个字符串。有没有更好的解决方案可以节省处理时间，比如MySQL触发器或类似的东西？

问插入8个随机字符的唯一字符串
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