Why same query runs on isqlplus but not in Forms/Reports trigger

Question

Hi,
I have one query in which I extract one column with parent table join if I run same query on isqlplus prompt it works but if I run same on Forms/Reports trigger it says found "select" where something else expected.
below is an example .
select em1.mreading, em1.grid_code,
(select em.mreading from energy_mreading em where em.grid_code=em1.grid_code and em.transformer_code=em1.transformer_code
and em.bus_bar=em1.bus_bar and to_date(to_char(em.r_date,'dd/mm/yyyy'),'dd/mm/yy') = to_date('02/01/07' ,'dd/mm/yy') - 1)
as Yreading
from energy_mreading em1
where to_date(to_char(em1.r_date,'dd/mm/yyyy'),'dd/mm/yy')= to_date('02/01/07' ,'dd/mm/yy')
Any one can help me, is there any restriction/limitations in Forms/Reports triggers.
Thanks, Khawar.

Answer 1

In forms and cursors you can not use scalar subqueries as you do. You have to use joins!
select
     em1.mreading
    ,em1.grid_code
    ,em.mreading as Yreading
from
    energy_mreading em1
   ,energy_mreading em
where 1=1
    and trunc(em1.r_date) = to_date('02/01/2007','dd/mm/rrrr')
    and em.grid_code = em1.grid_code
    and em.transformer_code = em1.transformer_code
    and em.bus_bar = em1.bus_bar
    and trunc(em.r_date) = trunc(em1.r_date) - 1
Try this, hope it works.