Hướng dẫn mysql random unique number

Possible Duplicate:
Algorithm for generating a random number

Hi i need to assign a randomly generated number to some entries into the database and it must be unique. I use:

$random_number = mt_rand[];
mysqli_query[$db_connection, "INSERT INTO my_table [rand_num, blabla] VALUES ['$random_number', '$blabla']"];

But ofc there could always be a slightly low chance that 2 random numbers will be the same. Then i could do something like:

function random_check[$random_number] {
    require_once['db_access.php'];
    $random_check = mysqli_query[$db_connection, "SELECT rand_num FROM my_table"];
    mysqli_close[$db_connection];
    $result = 1;
    while[$row = mysqli_fetch_array[$random_check]]{
            if [$row['rand_num'] == $random_number] {
             $result=0
           }
    }
        return $result;
};

$random_number = mt_rand[];
$random_check = random_check[$random_number];
if [$random_check == 0] {
      $random_number = mt_rand[];
}

But this would only check the number once and there will still be a chance that the new generated number already exists into the db.

Any suggestions? Thanks

asked Jan 12, 2012 at 11:41

3

Here is a method which you can use:

muya.dev
9061 gold badge13 silver badges33 bronze badges

 answered Jan 12, 2012 at 12:52
 
Vijeenrosh P.WVijeenrosh P.W
3591 gold badge3 silver badges7 bronze badges
Doing a SELECT rand_num FROM my_table and checking the resulting values is very, very inefficient. Use a WHERE clause:
do {
    $random_number = mt_rand[];
    $query_object = mysqli_query[$db_connection, "SELECT 1 FROM my_table WHERE rand_num = $random_number"];
    $query_record = mysqli_fetch_array[$query_object];
    if[! $query_record] {
        break;
    }
} while[1];
It is possible to write this code in lesser lines.
 answered Jan 12, 2012 at 12:12
 
Salman ASalman A
252k80 gold badges423 silver badges513 bronze badges
function random_check[$random_number] {
    require_once['db_access.php'];
    $random_check = mysqli_query[$db_connection, "SELECT rand_num FROM my_table"];
    mysqli_close[$db_connection];
    while[$row = mysqli_fetch_array[$random_check]]{
            if [$row['rand_num'] == $random_number] {
             return false;
           }
    }
    return true;
};

while[!random_check[mt_rand[]]{
    $myNumbber = random_check[mt_rand[];
}
--> Now u got unique number in "myNumber"
 answered Jan 12, 2012 at 11:45

2
md5[ strtotime["now"].$_SERVER['REMOTE_ADDR'] ];
strtotime["now"] would give you a unique number, but ifyou are using this script to process forms/uploads etc from multiple users, the ip address will just make certain of that [on the off chance that at the exact same second two entries are made... can that even happen?? hmm...]
md5[] cos i felt like it :D
 answered Jan 12, 2012 at
11:50
 
UmutUmut
666 bronze badges
4