I want to calculate day-to-day changes in a data set. In an ideal situation the following would suffice:
Date x
2007-01-01 5
2007-01-02 8
2007-01-03 4
2007-01-04 3
2007-01-05 10
2007-01-06 10
2007-01-07 2
2007-01-08 10
2007-01-09 1
2007-01-10 8

SELECT D1.date, (D1.x-D2.x)/D2.x AS change
FROM data AS D1 INNER JOIN data AS D2 ON D1.date=D2.date+1;

This will not work however for non-contiguous dates. In other words , what would be the suggested SQL query for a data set as follows ?

2007-01-01 5
2007-01-02 8
2007-01-03 4
2007-01-04 3
2007-01-05 10
2007-01-08 10
2007-01-09 2
2007-01-10 10
2007-01-11 1
2007-01-12 8

where day 6 and 7 constitute a weekend for which no samples are present. My initial thought would be to have a temporary table with the following structure : id - date - x
where id is a contiguous autonumber and the resulting query would be:

SELECT TD1.date, (TD1.x-TD2.x)/TD2.x AS change
FROM tempdata AS TD1 INNER JOIN tempdata AS TD2 ON TD1.id=TD2.id+1;

But the question is, how should this table be constructed, particularly because not all databases support autonumbers? Any other approaches which are perhaps more straightforward?