I have a table with column StartDate, I want to calculate the time difference between two consecutive record. 

Thanks. 

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@ Mark Byers and @ Yahia, I have request table as requestId, startdate 

```
requestId    startdate               
1            2011-10-16 13:15:56
2            2011-10-16 13:15:59
3            2011-10-16 13:15:59
4            2011-10-16 13:16:02
5            2011-10-16 13:18:07

```

and i want to know what is the time difference between requestid 1 & 2, 2 & 3, 3 & 4 and so on. i know i will need self join on table, but i am not getting correct on clause.