How to make unique random alphanumeric sequence in SQL Server - sql-server

Question

I want to make unique random alphanumeric sequence to be the primary key for a database table.
Each char in the sequence is either a letter (a-z) or number (0-9)
Examples for what I want :
kl7jd6fgw
zjba3s0tr
a9dkfdue3
I want to make a function that could handle that task!

Answer 1

You can use an uniqueidentifier. This can be generated with the NEWID() function:
SELECT NEWID()
will return something like:
BE228C22-C18A-4B4A-9AD5-1232462F7BA9

Answer 2

It is a very bad idea to use random strings as a primary key.
It will effect performance as well as storage size, and you will be much better of using an int or a bigint with an identity property.
However, generating a random string in SQL maybe useful for other things, and this is why I offer this solution:
Create a table to hold permitted char values.
In my example the permitted chars are 0-9 and A-Z.
CREATE TABLE Chars (C char(1))
DECLARE #i as int = 0
WHILE #i < 10
BEGIN
INSERT INTO Chars (C) VALUES (CAST(#i as Char(1)))
SET #i = #i+1
END
SET #i = 65
WHILE #i < 91
BEGIN
INSERT INTO Chars (C) VALUES (CHAR(#i))
SET #i = #i+1
END
Then use this simple select statement to generate a random string from this table:
SELECT TOP 10 C AS [text()]
FROM Chars
ORDER BY NEWID()
FOR XML PATH('')
The advantages:
You can easily control the allowed characters.
The generation of a new string is a simple select statement and not manipulation on strings.
The disadvantages:
This select results with an ugly name (i.e XML_F52E2B61-18A1-11d1-B105-00805F49916B). This is easily solved by setting the result into a local variable.
Characters will only appear once in every string. This can easily be solved by adding union:
example:
SELECT TOP 10 C AS [text()]
FROM (
SELECT * FROM Chars
UNION ALL SELECT * FROM Chars
) InnerSelect
ORDER BY NEWID()
FOR XML PATH('')
Another option is to use STUFF function instead of As [Text()] to eliminate those pesky XML tags:
SELECT STUFF((
SELECT TOP 100 ''+ C
FROM Chars
ORDER BY NEWID()
FOR XML PATH('')
), 1, 1, '') As RandomString;
This option doesn't have the disadvantage of the ugly column name, and can have an alias directly. Execution plan is a little different but it should not suffer a lot of performance lose.
Play with it yourself in this Sql Fiddle
If there are any more advantages / disadvantages you think of please leave a comment. Thanks.

Answer 3

NewID() Function will generate unique numbers.So i have incremented them with loop and picked up the combination of alpha numeric characters using Charindex and Left functions
;with list as
(
select 1 as id,newid() as val
union all
select id + 1,NEWID()
from list
where id + 1 < 100
)
select ID,left(val, charindex('-', val) - 2) from list
option (maxrecursion 0)

Answer 4

The drawback of NEWID() for this request is it limits the character pool to 0-9 and A-F. To define your own character pool, you have to role a custom solution.
This solution adapted from Generating random strings with T-SQL
--Define list of characters to use in random string
DECLARE #CharPool VARCHAR(255)
SET #CharPool = '0123456789abcdefghijkmnopqrstuvwxyz'
--Store length of CharPool for use later
DECLARE #PoolLength TINYINT
SET #PoolLength = LEN(#CharPool) --36
--Define random string length
DECLARE #StringLength TINYINT
SET #StringLength = 9
--Declare target parameter for random string
DECLARE #RandomString VARCHAR(255)
SET #RandomString = ''
--Loop control variable
DECLARE #LoopCount TINYINT
SET #LoopCount = 0
--For each char in string, choose random char from char pool
WHILE(#LoopCount < #StringLength)
BEGIN
SELECT #RandomString += SUBSTRING(#Charpool, CONVERT(int, RAND() * #PoolLength), 1)
SELECT #LoopCount += 1
END
SELECT #RandomString
http://sqlfiddle.com/#!6/9eecb/4354
I must reiterate, however, that I agree with the others: this is a horrible idea.