get extra rows for each group where date doesn't exist

Question

I've been playing with this for days, and can't seem to come up with something. I have this query:

select 
  v.emp_name as Name
  ,MONTH(v.YearMonth) as m 
  ,v.SalesTotal as Amount
from SalesTotals

Which gives me these results:

 Name         m         Amount
 Smith        1         123.50
 Smith        2          40.21
 Smith        3         444.21
 Smith        4          23.21
 Jones        1         121.00
 Jones        2         499.00
 Jones        3          23.23
 Jones        4          41.82
 etc....

What I need to do is use a JOIN or something, so that I get a NULL value for each month (1-12), for each name:

 Name         m         Amount
 Smith        1         123.50
 Smith        2          40.21
 Smith        3         444.21
 Smith        4          23.21
 Smith        5           NULL
 Smith        6           NULL
 Smith        ...         NULL
 Smith        12          NULL
 Jones        1         121.00
 Jones        2         499.00
 Jones        3          23.23
 Jones        4          41.82
 Jones        5           NULL
 Jones        ...         NULL
 Jones        12          NULL
 etc....

I have a "Numbers" table, and have tried doing:

select 
  v.emp_name as Name
  ,MONTH(v.YearMonth) as m 
  ,v.SalesTotal as Amount
from SalesTotals
   FULL JOIN Number n on n.Number = MONTH(v.YearMonth) and n in(1,2,3,4,5,6,7,8,9,10,11,12)

But that only gives me 6 additional NULL rows, where what I want is actually 6 NULL rows for each group of names. I've tried using Group By, but not sure how to use it in a JOIN statement like that, and not even sure if that's the correct route to take.

Any advice or direction is much appreciated!

Answer 1

Here's one way to do it:

select 
  s.emp_name as Name
  ,s.Number as m 
  ,st.salestotal as Amount
from (
  select distinct emp_name, number
  from salestotals, numbers 
  where number between 1 and 12) s left join salestotals st on 
    s.emp_name = st.emp_name and s.number = month(st.yearmonth)

• Condensed SQL Fiddle

Answer 2

You could do:

SELECT  EN.emp_name Name,
        N.Number M,
        ST.SalesTotal Amount
FROM (  SELECT Number 
        FROM NumberTable
        WHERE Number BETWEEN 1 AND 12) N
CROSS JOIN (SELECT DISTINCT emp_name
            FROM SalesTotals) EN
LEFT JOIN SalesTotals ST
    ON N.Number = MONTH(ST.YearMonth)
    AND EN.emp_name = ST.emp_name