[php] 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.

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.

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.

 <?php
    $hostname_conn = "localhost";
    $database_conn = "user_id";
    $username_conn = "root";
    $password_conn = "";
     $conn = mysql_pconnect($hostname_conn, $username_conn,   $password_conn) or trigger_error(mysql_error(),E_USER_ERROR); 
   mysql_select_db($database_conn,$conn);
   // 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);
    break;
    }   
}
  echo "inserted unique number into Data_base. use it as ID";
   ?>

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

USE IT

    $info = random_bytes(16);
    $info[6] = chr(ord($info[6]) & 0x0f | 0x40); 
    $info[8] = chr(ord($info[8]) & 0x3f | 0x80); 
    $result =vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($info), 4));
    return $result;

I use UUID() to create a unique value.

example:

insert into Companies (CompanyID, CompanyName) Values(UUID(), "TestUUID");

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 
WHERE  TABLE_SCHEMA = DATABASE() AND TABLE_NAME = "your_table";

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.

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.

DELIMITER $$

USE `temp` $$

DROP PROCEDURE IF EXISTS `GenerateUniqueValue`$$

CREATE PROCEDURE `GenerateUniqueValue`(IN tableName VARCHAR(255),IN columnName VARCHAR(255)) 
BEGIN
    DECLARE uniqueValue VARCHAR(8) DEFAULT "";
    DECLARE newUniqueValue VARCHAR(8) DEFAULT "";
    WHILE LENGTH(uniqueValue) = 0 DO
        SELECT CONCAT(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),
                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;
        DEALLOCATE PREPARE stmt;
    IF @rcount = 0 THEN
            SET uniqueValue = @newUniqueValue ;
        END IF ;
    END WHILE ;
    SELECT uniqueValue;
    END$$

DELIMITER ;

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

This generates random ids:

CREATE TABLE Persons (
    ID Integer PRIMARY KEY AUTOINCREMENT,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int
);

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.

If you use MySQL with version higher than 5.7.4, you can use the newly added RANDOM_BYTES function:

 SELECT TO_BASE64(RANDOM_BYTES(16));

This will result in a random string such as GgwEvafNLWQ3+ockEST00A==.

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.

https://developer.twitter.com/en/docs/basics/twitter-ids

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

Here it is the implementation for MySQL

https://github.com/EFTEC/snowflake-mysql

It consists of a function and a table.

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

it may help you...

$query=mysql_query("select * from collectors_repair");
$row=mysql_num_rows($query);
$ind=0;
if($row>0)
{
while($rowids=mysql_fetch_array($query))
{
  $already_exists[$ind]=$rowids['collector_repair_reportid'];
}
}
else
{
  $already_exists[0]="nothing";
}
    $break='false';
    while($break=='false'){
      $rand=mt_rand(10000,999999);

      if(array_search($rand,$alredy_exists)===false){
          $break='stop';
      }else{

      }
    }

 echo "random number is : ".$echo;

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

You might also consider using crypt()* to generate a [nearly-guaranteed] unique ID inside your contraints.