SQL Query issue find difference in records

Question

Hi All,
I am using oracle 10g. I need urgent help in finding difference in records based on date:
I have table sales as below:
salesman SALES_COUNT DATE
JOHN 20 04/01/2012
DENNY 15 04/01/2012
JOHN 30 04/02/2012
DENNY 30 04/02/2012
JOHN 45 04/03/2012
DENNY 50 04/03/2012
SALES_COUNT is increasing for sales man with date. Its like cumulative count. John has total sales from 04/01/2012 to 04/03/2012 is 50 and same case with Denny. This SALES_COUNT will keep on increasing with dates as sales keep adding in the table for each salesman.
But i want to have seprate counts for each salesman.
for e.g: SALES_COUNT JOHN on 04/02/2012 is 30-20 =10
SALES_COUNT JOHN on 04/03/2012 is 45-30 =15
SALES_COUNT DENNY on 04/02/2012 is 30-15 =15
SALES_COUNT JOHN on 04/03/2012 is 50-30 =20
Please help me with this scenario and let me know if need more information. I will greatly appreciate your help.
Thanks.

Answer 1

Does this give you what you want?
with t as (
     select 'JOHN' salesman, 20 sales_count, to_date('04/01/2012', 'mm/dd/yyyy') sale_date from dual
     union all
     select 'DENNY' salesman, 15 sales_count, to_date('04/01/2012', 'mm/dd/yyyy') sale_date from dual
     union all
     select 'JOHN' salesman, 30 sales_count, to_date('04/02/2012', 'mm/dd/yyyy') sale_date from dual
     union all
     select 'DENNY' salesman, 30 sales_count, to_date('04/02/2012', 'mm/dd/yyyy') sale_date from dual
     union all
     select 'JOHN' salesman, 45 sales_count, to_date('04/03/2012', 'mm/dd/yyyy') sale_date from dual
     union all
     select 'DENNY' salesman, 50 sales_count, to_date('04/03/2012', 'mm/dd/yyyy') sale_date from dual
select salesman,
       sales_count sales_todate,
       sale_date,
       sales_count - lag(sales_count, 1, 0) over (partition by salesman order by sale_date) daily_sales
from t
SALESMAN,SALES_TODATE,SALE_DATE,DAILY_SALES
DENNY,15,4/1/2012,15
DENNY,30,4/2/2012,15
DENNY,50,4/3/2012,20
JOHN,20,4/1/2012,20
JOHN,30,4/2/2012,10
JOHN,45,4/3/2012,15