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

Use LEFT JOIN instead with ISNULL to replace NULL with 0:

SELECT 
  list.listid, 
  ISNULL(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;

SQL Fiddle Demo

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Update

For SQL Server CE, try this:

SELECT 
  list.listid, 
  SUM(CASE WHEN customerlist.customerid IS NULL THEN 0 ELSE 1 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;