> Just found that on a particular case, SS FB 3.0.1 is about 4x slower than SC FB
> 2.5.2.
>
> Here is the query :
> ==========================
> select a.id,b.nm from tbl1 a, tbl2 b
> where a.id = b.id
> and a.id in (select c.id from tbl3 c)
>
> If the query change to this :
> ==========================
> select a.id,b.nm from tbl1 a, tbl2 b, tbl3 c
> where a.id = b.id
> and a.id = c.id
>
> SC FB 2.5.2 is about 1.3x faster than SS FB 3.0.1.

The queries are not really equivalent.

How about this query:

select a.id,b.nm
from tbl1 a
JOIN tbl2 b ON b.id = a.id
Where
EXISTS(
SELECT 1
FROM tbl3 c
WHERE
c.id = a.id
)