Question

I have a table that defines time intervals.

 _______________________________
| id | description | start_date |
|____|_____________|____________|
|  1 | First       |    NULL    |
|  3 | Third       | 2009-12-18 |
|  5 | Second      | 2009-10-02 |
|  4 | Last        | 2009-12-31 |
|____|_____________|____________|

It stores only the start date, the end date is a day before next date that follows.

I would like to have the next result:

 ____________________________________________
| id | description | start_date |  end_date  |
|____|_____________|____________|____________|
|  1 | First       |    NULL    | 2009-10-01 |
|  5 | Second      | 2009-10-02 | 2009-12-17 |
|  3 | Third       | 2009-12-18 | 2009-12-30 |
|  4 | Last        | 2009-12-31 |    NULL    |
|____|_____________|____________|____________|

How should I write this query, since a row contains values from other rows?

(I think MySQL function DATE_SUB could be useful.)

Answer 1

SELECT d.id, d.description, MIN(d.start_date), MIN(d2.start_date) - INTERVAL 1
DAY AS end_date
FROM start_dates d
LEFT OUTER JOIN start_dates d2 ON ( d2.start_date > d.start_date OR d.start_date IS NULL )
GROUP BY d.id, d.description
ORDER BY d.start_date ASC