Preventing ID duplication

Question

I am using this below. Will it prevent ID duplication?

Code:

$new_generating_id = on the process page this will be generating a new id for each time the process page is being processed;

  $sql = "select `Message_id` from `queries_sent` 
  where message_id='$new_generating_id'";
  $query = mysql_query($sql) or die ("Error: ".mysql_error());

  while ($row = mysql_fetch_array($query)){

$storedid = $row['Message_id'];


  }
  mysql_free_result($query);

  if ( $new_generating_id == $storedid ) {
echo("An error occured.");
    die('');
   } else {
echo('');
   }

To play around with it to see if it works, I tested it by using known variables.

I changed $new_generating_id to an id that exists and when the db pulled it it gave the error message. What do you guys think?

MySQL has a `unique` and `auto_increment` property for keys that should be used as IDs. You shouldn't be doing this in PHP. — Blender, Nov 28 '11 at 17:54
If you want integer values, consider auto increment field as Pekka says. If you just want a unique value, use PHP's inbuilt `uniqid()` function — Ayush, Nov 28 '11 at 17:55
I would recommend some `auto_increment` as well. If you don't want to or can't do that, maybe you could use the `uniqid` PHP built-in: [uniqid](http://php.net/manual/function.uniqid.php) — miku, Nov 28 '11 at 17:55
@pekka yes i have that thats for the field 'id' this is for another field called 'message_id' — Sam Khan, Nov 28 '11 at 17:58
@marcus if a post id already exists it should stop the form from inserting in the db the contents — Sam Khan, Nov 28 '11 at 17:58

score 1 · Answer 1 · edited Nov 28 '11 at 19:15

1

Try using a timestamp value for identification. It's unique for each transaction submitted. the simplest form is:

$id='myid'.time();

Here I've used the string myid and concatenated it with the timestamp value (from the time() function). Now store this value in the database and perform operations on it.

edited Nov 28 '11 at 19:15

William

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answered Nov 28 '11 at 18:11

geeky_bat

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How come time() is 'unique for each transaction submitted' ? Unless you are 100% sure you have no more than 1tps. – Mchl Nov 28 '11 at 19:21

score 0 · Answer 2 · answered Nov 28 '11 at 18:24

if you want to insert some unique string into the Message_id field, first mark the Message_id as unique in the table. then you can use something like this code to insert new ids into that table:

do {
    $uniqueId = md5(uniqid(mt_rand(), true));
    mysql_query("INSERT INTO queries_sent (Message_id) VALUES ('$uniqueId')");
} while (mysql_errno() == 1062);

Preventing ID duplication

2 Answers2