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How to generate unique id in MySQL?

I'm programming a script using PHP and MySQL and I want to get a unique id (consisting of a string: capitals and small letters with numbers) like: gHYtUUi5b. I found many functions in PHP that can generate such numbers but I'm afraid about how to ensure the id is unique!

UPDATE: uuid is long, I mean such id like: (P5Dc) an 11 alphanumeric char.

I use UUID() to create a unique value.


insert into Companies (CompanyID, CompanyName) Values(UUID(), "TestUUID");
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You may like the way that we do it. I wanted a reversible unique code that looked "random" -a fairly common problem.

  • We take an input number such as 1,942.
  • Left pad it into a string: "0000001942"
  • Put the last two digits onto the front: "4200000019"
  • Convert that into a number: 4,200,000,019

We now have a number that varies wildly between calls and is guaranteed to be less than 10,000,000,000. Not a bad start.

  • Convert that number to a Base 34 string: "2oevc0b"
  • Replace any zeros with 'y' and any ones with 'z': "2oevcyb"
  • Upshift: "2OEVCYB"

The reason for choosing base 34 is so that we don't worry about 0/O and 1/l collisions. Now you have a short random-looking key that you can use to look up a LONG database identifier.

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    • I forgot - if you add 1,000,000,000 to the number after converting it back the first time, then you avoid the YYYYYYYY5 problem (mangling bases means that a large enough non-regular base number will look sufficiently random). Just don't forget to subtract it out on the way back :)

A programmatic way can be to:

  • add a UNIQUE INDEX to the field
  • generate a random string in PHP
  • loop in PHP ( while( ! DO_THE_INSERT ) )
    • generate another string


  • This can be dirty, but has the advantage to be DBMS-agnostic
  • Even if you choose to use a DBMS specific unique ID generator function (UUID, etc) it is a best practice to assure the field HAS to be UNIQUE, using the index
  • the loop is statistically not executed at all, it is entered only on insert failure
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    • Unless of course your random number generator isn't completely random. Written race conditions are usually a Bad Idea ^TM
    • Rather than looping on failed insert (which can be caused by other reasons thus causing infinite loop), I'd loop the ID generation on finding the same ID, then insert and throw an exception on insert fail. You have the same statistic of only one loop, it's safer and provide information when the insert fails (for other reasons).
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    • this way you are using 2 DB operations, being no more atomic. Better to check the reason of the failure inside the loop, once the failure is already occurred.
    • this the only solution in my mind, even before i post my question. is the way use resources. and at the same time isn't scientific.
    • It is instead. If well implemented it is as safe as the DBMS based approach, resources are not a matter as if you generate a random string the probability of an INSERT fail is very very low (depending on the table dimension of course), so you loop is actually a single operation.

How you generate the unique_ids is a useful question - but you seem to be making a counter productive assumption about when you generate them!

My point is that you do not need to generate these unique id's at the time of creating your rows, because they are essentially independent of the data being inserted.

What I do is pre-generate unique id's for future use, that way I can take my own sweet time and absolutely guarantee they are unique, and there's no processing to be done at the time of the insert.

For example I have an orders table with order_id in it. This id is generated on the fly when the user enters the order, incrementally 1,2,3 etc forever. The user does not need to see this internal id.

Then I have another table - unique_ids with (order_id, unique_id). I have a routine that runs every night which pre-loads this table with enough unique_id rows to more than cover the orders that might be inserted in the next 24 hours. (If I ever get 10000 orders in one day I'll have a problem - but that would be a good problem to have!)

This approach guarantees uniqueness and takes any processing load away from the insert transaction and into the batch routine, where it does not affect the user.

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    • "What I do is pre-generate unique id's for future use, that way I can take my own sweet time and absolutely guarantee they are unique" How do you know the id doesn't already exist in the DB unless you check at insertion time?

Use UUID function.

I don't know the source of your procedures in PHP that generates unique values. If it is library function they should guarantee that your value is really unique. Check in documentation. You should, hovewer, use this function all the time. If you, for example, use PHP function to generate unique value, and then you decide to use MySQL function, you can generate value that already exist. In this case putting UNIQUE INDEX on the column is also a good idea.

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USE `temp` $$

DROP PROCEDURE IF EXISTS `GenerateUniqueValue`$$

CREATE PROCEDURE `GenerateUniqueValue`(IN tableName VARCHAR(255),IN columnName VARCHAR(255)) 
    DECLARE uniqueValue VARCHAR(8) DEFAULT "";
    DECLARE newUniqueValue VARCHAR(8) DEFAULT "";
    WHILE LENGTH(uniqueValue) = 0 DO
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1),
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1),
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1),
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1),
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1),
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1),
                SUBSTRING('ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789', RAND()*34+1, 1)
                ) INTO @newUniqueValue;
        SET @rcount = -1;
        SET @query=CONCAT('SELECT COUNT(*) INTO @rcount FROM  ',tableName,' WHERE ',columnName,'  like ''',newUniqueValue,'''');
        PREPARE stmt FROM  @query;
        EXECUTE stmt;
    IF @rcount = 0 THEN
            SET uniqueValue = @newUniqueValue ;
        END IF ;
    SELECT uniqueValue;


And call the stored procedure as GenerateUniqueValue('tableName','columnName'). This will give you a 8 digit unique character everytime.

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Below is just for reference of numeric unique random id...

it may help you...

$query=mysql_query("select * from collectors_repair");



 echo "random number is : ".$echo;

and you can add char with the code like -> $rand=mt_rand(10000,999999) .$randomchar; // assume $radomchar contains char;

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For uniqueness what I do is I take the Unix timestamp and append a random string to it and use that.

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    • u can use microtime and convert it to hex to get the string effect or atleast in most cases , this would work ok if u dont have high volume traffic / insertions in db.
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    • "i use it to access recourse through url, if i use auto_increment it will be easy to suggest" .. keeping that in mind... if insertions are high .. you can do it the other way around .. use auto increment to add normal ids in the DB .. on the site , where you display the links , have the id encrypted with a known key and then decrypt it back with that key before making the DB query.
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    • if u are already using this .. i would suggest keep it this way .. i have no idea how much traffic u have or the db size .. but keep in mind that varchar type look ups are slower than integer look ups and re-indexing on inserts/updates is costly as well. ideally to avoid calculating the hash each time .. just create another field in the db which stores this hash .. show that hash to the user from there..atleast that would avoid the encryption part each time the link needs to be displayed. i personally prefer putting more load on the php end rather than mysql.
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    • i agree with you 80%, but i think there are other solution used by large site like: youtube to keep id simple and short..
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    • youtube stores its data on CDNs , no one really know how they generate the unique ID .. but my guess is that unique ID contains not only the record ID but the server/cluster/CDN addressing as well .. so that unique ID is basically a composite of more than 1 values, which is decrypted into a more meaningful and fuller explanation of the record and its location.
    $hostname_conn = "localhost";
    $database_conn = "user_id";
    $username_conn = "root";
    $password_conn = "";
     $conn = mysql_pconnect($hostname_conn, $username_conn,   $password_conn) or trigger_error(mysql_error(),E_USER_ERROR); 
   // run an endless loop      
    while(1) {       
    $randomNumber = rand(1, 999999);// generate unique random number               
    $query = "SELECT * FROM tbl_rand WHERE the_number='".mysql_real_escape_string ($randomNumber)."'";  // check if it exists in database   
    $res =mysql_query($query,$conn);       
    $rowCount = mysql_num_rows($res);
     // if not found in the db (it is unique), then insert the unique number into data_base and break out of the loop
    if($rowCount < 1) {
    $con = mysql_connect ("localhost","root");      
    mysql_select_db("user_id", $con);       
    $sql = "insert into tbl_rand(the_number) values('".$randomNumber."')";      
    mysql_query ($sql,$con);        
    mysql_close ($con);
  echo "inserted unique number into Data_base. use it as ID";
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crypt() as suggested and store salt in some configuration file, Start salt from 1 and if you find duplicate move to next value 2. You can use 2 chars, but that will give you enough combination for salt.

You can generate string from openssl_random_pseudo_bytes(8). So this should give random and short string (11 char) when run with crypt().

Remove salt from result and there will be only 11 chars that should be enough random for 100+ millions if you change salt on every fail of random.

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To get unique and random looking tokens you could just encrypt your primary key i.e.:

SELECT HEX(AES_ENCRYPT(your_pk,'your_password')) AS 'token' FROM your_table;

This is good enough plus its reversable so you'd not have to store that token in your table but to generate it instead.

Another advantage is once you decode your PK from that token you do not have to do heavy full text searches over your table but simple and quick PK search.

Theres one small problem though. MySql supports different block encryption modes which if changed will completely change your token space making old tokens useless...

To overcome this one could set that variable before token generated i.e.:

SET block_encryption_mode = 'aes-256-cbc';

However that a bit waste... The solution for this is to attach an encryption mode used marker to the token:

SELECT CONCAT(CONV(CRC32(@@GLOBAL.block_encryption_mode),10,35),'Z',HEX(AES_ENCRYPT(your_pk,'your_password'))) AS 'token' FROM your_table;

Another problem may come up if you wish to persist that token in your table on INSERT because to generate it you need to know primary_key for the record which was not inserted yet... Ofcourse you might just INSERT and then UPDATE with LAST_INSERT_ID() but again - theres a better solution:

INSERT INTO your_table ( token )
SELECT CONCAT(CONV(CRC32(@@GLOBAL.block_encryption_mode),10,35),'Z',HEX(AES_ENCRYPT(your_pk,'your_password'))) AS 'token'
FROM information_schema.TABLES 

One last but not least advantage of this solution is you can easily replicate it in php, python, js or any other language you might use.

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You could use Twitter's snowflake.

In short, it generates a unique id based on time, server id and a sequence. It generates a 64-bit value so it is pretty small and it fits in an INT64. It also allows for sorting values correctly.


In sum, it allows multiple servers, highly concurrency, sorting value and all of them in 64 bits.

Here it is the implementation for MySQL


It consists of a function and a table.

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Warm tip !!!

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