JOIN query works with 3.23 but not 4.0.13

[tunahan]

Hi,
I have a simple join query below which queries the name of schools with count of
student numbers for each school from two tables School,Student.
select sc.name,
Sum(if(student.SNO is not null, 1, 0)) nmbr,
from school sc
left outer join student
on sc.school_id = student.school_id
group by sc.school_id
this runs just 0.30 sec with Mysql3.23 but 30Sec with Mysql 4.0.13.
i could not find a solution.But i suspect from NULL threatment.
tonBalik