Question

I have a database where everything is versioned inside itself using start_date and end_date

What I want to do is dynamically get a version number for a row.

So, get all rows with a particular item_id ordered by start_date and then given a start_date and end_date that will isolate it down to one row. what I want is to find out where that row sits.

e.g. the data

id | item_id | start_date
1  | 1       | 01-31-2012
2  | 1       | 02-31-2012
3  | 2       | 02-31-2012
4  | 1       | 03-31-2012
5  | 2       | 05-31-2012
6  | 1       | 04-31-2012

if using select id from items where item_id = 2 and start_date = 05-31-2012

would return 5 so what I would want for the version would be 2

if using select id from items where item_id = 1 and start_date = 03-31-2012

would return 4 so what I would want for the version would be 3

The only way I can think of to do this would be to select all rows with the item_id of whatever, and then loop over each item checking the start_date, if it is not what I want increase version_number by 1.

Is there a way to do it with just mysql?

Answer 1

SELECT COUNT(*) version
FROM items
WHERE item_id = 2 AND start_date <= '2012-05-31'

or id <= 5 instead of date comparison (assuming id is unique and grows monotonously)