Generating random strings with T-SQL

Question

If you wanted to generate a pseudorandom alphanumeric string using T-SQL, how would you do it? How would you exclude characters like dollar signs, dashes, and slashes from

Answer 1

This uses rand with a seed like one of the other answers, but it is not necessary to provide a seed on every call. Providing it on the first call is sufficient.

This is my modified code.

IF EXISTS (SELECT * FROM sys.objects WHERE type = 'P' AND object_id = OBJECT_ID(N'usp_generateIdentifier'))
DROP PROCEDURE usp_generateIdentifier
GO

create procedure usp_generateIdentifier
    @minLen int = 1
    , @maxLen int = 256
    , @seed int output
    , @string varchar(8000) output
as
begin
    set nocount on;
    declare @length int;
    declare @alpha varchar(8000)
        , @digit varchar(8000)
        , @specials varchar(8000)
        , @first varchar(8000)

    select @alpha = 'qwertyuiopasdfghjklzxcvbnm'
        , @digit = '1234567890'
        , @specials = '_@#$&'
    select @first = @alpha + '_@';

    -- Establish our rand seed and store a new seed for next time
    set  @seed = (rand(@seed)*2147483647);

    select @length = @minLen + rand() * (@maxLen-@minLen);
    --print @length

    declare @dice int;
    select @dice = rand() * len(@first);
    select @string = substring(@first, @dice, 1);

    while 0 < @length 
    begin
        select @dice = rand() * 100;
        if (@dice < 10) -- 10% special chars
        begin
            select @dice = rand() * len(@specials)+1;
            select @string = @string + substring(@specials, @dice, 1);
        end
        else if (@dice < 10+10) -- 10% digits
        begin
            select @dice = rand() * len(@digit)+1;
            select @string = @string + substring(@digit, @dice, 1);
        end
        else -- rest 80% alpha
        begin
            select @dice = rand() * len(@alpha)+1;

            select @string = @string + substring(@alpha, @dice, 1);
        end

        select @length = @length - 1;   
    end
end
go