Should i use nested SQL Statements? or PL/SQL?

Question

here is my table:
let's call this table total_stats, with 2 fields (columns) Date and Total.
Row | Total
ROW1 | 12508
ROW2 | 12526
I am going crazy trying to write some sql or pl/sql that will give me the following results: the result of row2Total - row1Total. I need the delta of the two Total's rows.
Is there an easy way to do this without writing multiple nested sql statments?
Should i write a procedure that uses cursors to help me get my end result?
thanks

Answer 1

Use analytic functions - LAG and LEAD - to access other rows in the result set in a current row. This should get you started:
SQL> create table total_stats as
  2  select sysdate-1 as some_date, 12508 as some_value from dual
  3  union all
  4  select sysdate as some_date, 12526 as some_value from dual
  5  /
Table created.
SQL> select * from total_stats;
SOME_DATE  SOME_VALUE
12/11/2007      12508
13/11/2007      12526
2 rows selected.
SQL> select
  2    some_date,
  3    some_value as this_dates_value,
  4    lag(some_value) over (order by some_date) as the_previous_dates_value
  5  from
  6    total_stats
  7  /
SOME_DATE  THIS_DATES_VALUE THE_PREVIOUS_DATES_VALUE
12/11/2007            12508
13/11/2007            12526                    12508
2 rows selected.