Generate unique random numbers using SQL - sql

Question

I have some SQL code which generates random numbers using the following technique:
DECLARE #Random1 INT, #Random2 INT, #Random3 INT, #Random4 INT, #Random5 INT, #Random6 INT, #Upper INT, #Lower INT
---- This will create a random number between 1 and 49
SET #Lower = 1 ---- The lowest random number
SET #Upper = 49; ---- The highest random number
with nums as (
select #lower as n
union all
select nums.n+1
from nums
where nums.n < #Upper
),
randnums as
(select nums.n, ROW_NUMBER() over (order by newid()) as seqnum
from nums
)
select #Random1 = MAX(case when rn.seqnum = 1 then rn.n end),
#Random2 = MAX(case when rn.seqnum = 2 then rn.n end),
#Random3 = MAX(case when rn.seqnum = 3 then rn.n end),
#Random4 = MAX(case when rn.seqnum = 4 then rn.n end),
#Random5 = MAX(case when rn.seqnum = 5 then rn.n end),
#Random6 = MAX(case when rn.seqnum = 6 then rn.n end)
from randnums rn;
select #Random1, #Random2, #Random3, #Random4, #Random5, #Random6
My question is how random is this number generation? and is there another way to do this which is more "random".
I am using:
Microsoft SQL Server 2008 (SP3) - 10.0.5512.0 (X64) Aug 22 2012 19:25:47 Copyright (c) 1988-2008 Microsoft Corporation Developer Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1)
The problem with most solutions is you'll end up with values like this: 14,29,8,14,27,27 I cannot have duplicate numbers!

Answer 1

I guess you could do something like this much simpler and much easier
DECLARE #Upper INT;
DECLARE #Lower INT;
SET #Lower = 1; /* -- The lowest random number */
SET #Upper = 49; /* -- The highest random number */
SELECT #Lower + CONVERT(INT, (#Upper-#Lower+1)*RAND());
For getting a random number without repetition, this will do the job
WITH CTE
AS
(
SELECT randomNumber, COUNT(1) countOfRandomNumber
FROM (
SELECT ABS(CAST(NEWID() AS binary(6)) %49) + 1 randomNumber
FROM sysobjects
) sample
GROUP BY randomNumber
)
SELECT TOP 5 randomNumber
FROM CTE
ORDER BY newid()
To set the highest limit, you can replace 49 with your highest limit number.

Answer 2

For Laravel:
public function generatUniqueId()
{
$rand = rand(10000, 99999);
$itemId = $rand;
while (true) {
if (!BookItem::whereBookItemId($itemId)->exists()) {
break;
}
$itemId = rand(10000, 99999);
}
return $itemId;
}

Answer 3

Create a list of random numbers. For this example I did 100, could be more, could be less (but no less than your limit)
Use row_number() function to detect duplicates
Once you delete the duplicates, select top 6 number in your list
with RandomNumbers as
(
select id = 1, number = round(((56 - 1 -1) * RAND(CHECKSUM(NEWID())) + 1), 0),
orderid = round(((56 - 1 -1) * RAND(CHECKSUM(NEWID())) + 1), 0)
union all
select id + 1, round(((56 - 1 -1) * RAND(CHECKSUM(NEWID())) + 1), 0), round(((56 - 1 -1) * RAND(CHECKSUM(NEWID())) + 1), 0)
from RandomNumbers where id < 100
),
NoDuplicates as
(
select number, id = row_number() over (partition by number orderid by order) from
(
select numeber, order, repeat = row_number() over (partition by numeber orderid by order)
from RandomNumbers
) a
where repeat = 1
)
select * from NoDuplicates where id <= 6

Answer 4

You can use Rand() function .
select CEILING(RAND() *<max of random numbers))