"Where" condition containing ...in (select ...)

[Majdi Swais]

I'm trying to execute the following query
"select f1,f2 from table1 where f2 in (select f3 from table2 where ...)"

This query takes too much time to execute especially when table1 contains thousands of rows. If I execute "select f3 from table2 where ...", store the results in an array (r1,r2,...,rn) and rewrite the query as:
"select f1,f2 from table1 where f2 in (r1,r2,...,rn)", the query will execute very fast (as expected)
Note: both f2 and f3 are integers and indexed

Regards