SQL - How to Calculate Differences Between Values for GUIDs Within Date Ranges

Data and Databases
1

I have a dataset organized as follows: the columns are [date], [guid], and [value (int)]. Here’s an example of the data structure:

[date], [guid], [value]
10/1, guid1, 10
10/1, guid2, 5
10/2, guid1, 12
10/2, guid2, 14
10/3, guid1, 11

I am looking to extract results that show the difference in values for the same GUIDs across consecutive days. For instance, the desired outcome would look like this:

10/1, guid1, 2
10/1, guid2, 9
10/2, guid1, -1

This means for each GUID, I’m comparing today’s value against the value from the next day, then calculating the difference. For example, for the entry 10/1 and guid1, the calculation is:

10/1, guid1, 10
10/2, guid1, 12

Thus, the result for 10/1, guid1 is 12 - 10 = 2. How can I achieve this in SQL? Thanks!

2

Why not try using the LEAD or LAG functions? They’re great for comparing adjacent rows. You could PARTITION by GUID and ORDER by date to get next day’s value, then calculate difference easily. Anyone else think this approach might work or see any challenges with it? :thinking:

3

I would suggest attempting a self-join approach. You can join the dataset on itself where date + 1 from the first dataset matches date from the second, ensuring both entries have the same guid. This way, you directly get the adjacent day’s value for each guid. Once you have this, you can compute the difference between the value of the current day and the joined day’s value. While this method can be a bit more complex, it gives you control over the joins you’re establishing, which can be useful for customized or complex queries.

4

You could also consider using a subquery to first calculate the diffrences. If you select the current day’s guid and values, and then in a subquery get the value for the next day, you can minus them right in the primary select’s column. It’s simple but can be quite effective too.

5

Has anyone tried using window functions other than LEAD or LAG for this task? Like combining ROW_NUMBER with a self-join could offer an alternative way to align and compare rows. Does anyone think such a method might help tackle this problem differently? :thinking:

6

Another approach you might consider is using a common table expression (CTE) to precompute the previous day’s value for each GUID. This can be achieved by creating a sequence of days and joining it with your data based on GUID and date conditions. With this method, you can smoothly handle comparisons without cluttering the main query, keeping it clean and comprehensive. Especially useful when working with complex datasets requiring preliminary calculations for clarity during the main data processing steps.