Oracle Trigger to compare between current month and previous

I have the following table: -
tbl_EmpMonthSalaries
fld_EmpId
fld_Alw_Ded_Tag
fld_Alw_Ded_Id
fld_Alw_Ded_Amount
fld_FromPeriod
fld_ToPeriod

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I need help in write Oracle trigger to make the following: -
Create new table to store result there
Make compare between current month allwances and deduction with last allwances and deductions withdraw the same employee
If there any different should store the result in a new Table like
fld_EmpId
fld_AlwDedTag
fld_AlwDedId
fld_FromPeriod
fld_ToPeriod
fld_AlwDedAmount
fld_OldFromPeriod
fld_OldToPeriod
fld_OldAlwded

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Each time run this trigger delete the new table and recreated again
The trigger should be run after commit done (That only one time)

Any help
egovernmentAsked:
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flow01Commented:
try this query first, if it works you can make a view of it

fld_EmpId
,fld_Alw_Ded_Tag
,fld_Alw_Ded_Id
,fld_FromPeriod
,fld_ToPeriod
,fld_Alw_Ded_Amount fld_AlwDedAmount -- why diffirent name her
,lag(FromPeriod) OVER (PARTITION BY fld_EmpId ORDER BY fld_FromPeriod) fld_OldFromPeriod
,lag(fld_ToPeriod) OVER (PARTITION BY fld_EmpId ORDER BY fld_FromPeriod) fld_OldToPeriod
,lag(fld_Alw_Ded_Amount) OVER (PARTITION BY fld_EmpId ORDER BY fld_FromPeriod) fld_OldAlwded
from tbl_EmpMonthSalaries

if you still want the new_table

create trigger xx
AFTER INSERT OR UPDATE OR DELETE
on  tbl_EmpMonthSalaries
is
begin
   delete from new_table; -- but it should exist the first time
   -- execute immediate 'truncate new_table'  -- will be fast but i don't know if allowed here
   insert into new_table
   -- same query as before
   select ...;
end;

-- you can't do it on commit : this is a statement trigger it will fire for each insert, insert,update,delete
-- if could worry about performance
-- create a package with an id-list to hold the id's action is necessary
in a before delete for each row trigger add the :old.fld_EmpId to the list
in a before insert, update for each row trigger add the  :new.fld_EmpId to the list
in the after statement trigger
delete the rows with id's that are in the list  and add new records base on the id-list
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egovernmentAuthor Commented:
I don't need to write a query or view I need a trigger
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flow01Commented:
You want to achieve a goal, a trigger might be 1 way to achieve it. I suggested another way, not knowing your goal.
But there is also a trigger in my post:
see create trigger
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