Thanks in advance to anyone who can help me with this.

I have a view (lets call it V_VIEW).

When I run a query like this:
select * from V_VIEW where ID = X
it is SLOW

But if I don't use the view, and just take the SQL that makes up
V_VIEW and put the "where ID = X" into that SQL, it is FAST

any idea why that would happen?

V_VIEW looks like sort of like this:

select ID, A, B, t2.C, sum(t2.D)
from table1 t1
left join table2 t2 on t1.ID = t2.ID
group by ID, A, B, C