tmpid	password               morestuff
1      BSLPYRZPOAH8LDCW19MJ    one
2      T2OD2LLJC9IPWLNEOIJE    two
3      C3U4KN5NHSXEIGOZ6BGH    three

Create View OneRandomString20
AS 

with
a1 as (select 1 as N union all
       select 1 union all
       select 1 union all
       select 1 union all
       select 1 union all
       select 1 union all
       select 1 union all
       select 1 union all
       select 1 union all
       select 1),
a2 as (select
            1 as N
       from
            a1 as a
            cross join a1 as b),
a3 as (select
            1 as N
       from
            a2 as a
            cross join a2 as b),
a4 as (select
            1 as N
       from
            a3 as a
            cross join a2 as b),
Tally as (select
            row_number() over (order by N) as N
          from
            a4)
, cteRandomString (
    RandomString
) as (
select top (20)
    substring(x,(abs(checksum(newid()))%36)+1,1)
from
    Tally cross join (select x='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ') a
)
 select 
replace((select
    ',' + RandomString
from
    cteRandomString
for xml path ('')),',','') AS Results;

GO
CREATE FUNCTION fn_RandomString()
returns varchar(20)
AS
BEGIN
Declare @results varchar(20)
SELECT top 1 @results = Results from OneRandomString20
return @results
END
GO
select dbo.fn_RandomString()

CREATE TABLE tmp(tmpid int identity(1,1) not null primary key,password varchar(20) default(dbo.fn_RandomString()),morestuff varchar(30) )
insert into tmp(morestuff)
select 'one' union all select 'two' union all select 'three'
select * from tmp

create view dbo.MyNewID as
select newid() as NewIDValue;
go
create function dbo.ufn_RandomString(
    @pStringLength int = 20
) returns varchar(max)
as begin
    declare  @RandomString varchar(max);
    with
    a1 as (select 1 as N union all
           select 1 union all
           select 1 union all
           select 1 union all
           select 1 union all
           select 1 union all
           select 1 union all
           select 1 union all
           select 1 union all
           select 1),
    a2 as (select
                1 as N
           from
                a1 as a
                cross join a1 as b),
    a3 as (select
                1 as N
           from
                a2 as a
                cross join a2 as b),
    a4 as (select
                1 as N
           from
                a3 as a
                cross join a2 as b),
    Tally as (select
                row_number() over (order by N) as N
              from
                a4)
    , cteRandomString (
        RandomString
    ) as (
    select top (@pStringLength)
        substring(x,(abs(checksum((select NewIDValue from MyNewID)))%36)+1,1)
    from
        Tally cross join (select x='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ') a
    )
     select @RandomString = 
    replace((select
        ',' + RandomString
    from
        cteRandomString
    for xml path ('')),',','');
    return (@RandomString);
end
GO