How to get the summation of a record over time

Question

i have a database. i insert salary every month into my table.i want the total of each employee's salary to be populated in another table, so that at the end of every month, i will have the current total salary of each employee populating this table which will be there as another data. when i insert the value into a column of a table (such as employees table), i want the current value to be added automatically to the previous value such that at the end of every month i will know the total salary received by each employee just by looking at this table.
how do i achieve this objective?
thanks.

Answer 1

this example might be of help:
SQL> select * from emp_sal_log;
EMPNO SAL_DATE      SALARY
A     09-AUG-06       1400
A     23-AUG-06       1500
A     06-SEP-06       1600
A     20-SEP-06       1700
B     20-SEP-06       1600
SQL> declare
  2    cursor c1 is
  3     select a.empno, a.sal_date, a.salary, a.rowid,
  4            row_number() over (partition by a.empno order by a.sal_date) rn
  5       from emp_sal_log a;
  6 
  7    vRnCtr     Number := 0;
  8    vPrevRowId Varchar2(40);
  9  begin
10    for c1_rec in c1 loop
11      vRnCtr := c1_rec.rn + 1;
12      if c1_rec.rn = 1 then
13        -- nothing to process since it is the first transaction
14        -- for a given employee
15        null;
16      else
17        update emp_sal_log
18           set salary = salary + c1_rec.salary
19         where rowid  = vPrevRowID;
20        commit;
21      end if;
22      vPrevRowId := c1_rec.rowid;
23    end loop;
24  end;
25  /
PL/SQL procedure successfully completed.
SQL> select * from emp_sal_log;
EMPNO SAL_DATE      SALARY
A     09-AUG-06       2900
A     23-AUG-06       3100
A     06-SEP-06       3300
A     20-SEP-06       1700
B     20-SEP-06       1600
SQL>