Reference to preceding row

Please look at the following example, where we measure the size of some kids:

SELECT name, measurement_date, size FROM kids WHERE name = 'Bill' ORDER BY 1,2;

Bill | 2007-01-01 | 90
Bill | 2007-05-01 | 95
Bill | 2007-12-01 | 101

How can I rewrite the query that it gives me the growth since the last measurement? Like this:

Bill | 2007-01-01 | 90 | (null)
Bill | 2007-05-01 | 95 | 5
Bill | 2007-12-01 | 101 | 6

There are surely many ways to do this, but what is the best / easiest approach?

Thanks and best,

Hans Received on Mon Jun 08 2009 - 10:56:25 CDT