How to make unique random alphanumeric sequence in 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)

Answer 1

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.