I have multiple applications each with unique application ID's, Each application has logs which are stored in a table. I want to know how to calculate the date difference
eg:

```
    AppID Start           Loggedon   change 
    A1    08/07/2010      08/09/2010 Xchange
    A1    08/07/2010      08/20/2010 Ychange
    A1    08/07/2010      08/30/2010 Zchange
    A2    07/07/2010      07/13/2010 Ychange
    A3    09/07/2010      09/09/2010 Xchange

```

So I want the values 

```
Difference
2   (Difference between the application start date and 1st loggedon date)
11  (difference between 08/20 and 08/09, the prior row because AppID stayed the same)
10  (difference between 08/30 and 08/20, the prior row because AppID stayed the same)
6   (Difference between the application start date and 1st loggedon date)
2   (Difference between the application start date and 1st loggedon date)

```

Hope I am clear. How can I achieve this, I tried Ranking and Row\_Number. But I might be wrong somewhere. I am using SQL Server and cannot use LAG()