Question

With this query, I get a result that is two short of the table because they are not included in count, and I would like get the NULL values in the result. To do this, I am pretty sure I need to use a subquery of some kind, but I am not sure how, since the attribute in question is an aggregate.

SELECT Equipment.SerialNo , Name, COUNT(Assignment.SerialNo) 
FROM Equipment
INNER JOIN Assignment
     ON Assignment.SerialNo = Equipment.SerialNo

GROUP BY Equipment.SerialNo, Name

Answer 1

You need to change your inner join to a left outer join and count something other than Assignment.SerialNo if you want all rows counted — use count(*) or another property that will not be null, as count(column) does not include nulls for that column. If you don’t want null Assignment.SerialNo values included in the count, then continue aggregating on that column.

An inner join by definition will skip values where Assignment.SerialNo is NULL— an outer join will include them.