How to create a new column and group by that column in a selection?

[Ifor]

Is this statement correct?

You need to understand the logical order of query processing. eg: With your examples, if Cancelled is in Table2 (and you should really have written Table2.Cancelled or used an alias) then your second query will effectively convert the LEFT OUTER JOIN to an INNER JOIN as the NULLs from the LEFT OUTER JOIN will never be equal to 'Y'. Create some test data and see what happens.