I've got 2 MySQL tables: Employees, and Mileage.  Mileage records trips
employees and there may be 0 or more Mileage rows for each Employee
row.  The Mileage table has a trip_date column. For testing purposes,
trip_date column in all rows is set to 2002-03-01.

There are currently 15 rows in the Employees table.

I want the result of the following select to be 15 rows (1 for each
employee, whether or not there are any rows in the Mileage table for
employee).  If I take the "where" clause out, I get all 15 rows
a number of rows where sum(m.miles) = 0 (which is what I want).  If I
the "where" clause in, however, I don't get employees with sum(m.miles)
= 0
(even though the "where" clause should include all of the Mileage rows).
(Only 3 Employees actually have corresponding rows in the Mileage table,
and I only get 3 rows back.)

select e.id,lname,sum(m.miles) from employees e
     left join mileage m on e.id=m.id
where month(m.trip_date) = 3
       and substring(year(m.trip_date),3,2) = '02'
     group by e.id;

I need to select by month/year from the Mileage table.  Any idea how the
"select" can be modified to include rows for all of the Employees?

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