SQL Joining by field that *may* be empty

Question

In my SQL CE database I have three tables: customer, list and customerlist (a junction table between customer and list<

Answer 1

You must use LEFT JOIN syntax.

select list.listid,  case when count(customerlist.customerid) is null then 0 else count(customerlist.customerid) end as numppl, list.ShortDesc
from list left join customerlist on list.listid=customerlist.listid
group by list.ShortDesc, list.listid
order by numppl desc

Or you can use RIGHT JOIN :

select list.listid, case when count(customerlist.customerid) is null then 0 else count(customerlist.customerid) end as numppl, list.ShortDesc
from customerlist right join list on customerlist.listid=list.listid
group by list.ShortDesc, list.listid
order by numppl desc

Use COALESCE :

select list.listid,  coalesce(count(customerlist.customerid),0) as numppl, list.ShortDesc
from list left join customerlist on list.listid=customerlist.listid
group by list.ShortDesc, list.listid
order by numppl desc