Set of datetime versioned rows, how to build the most up to date row

Question

I created this SQL fiddle with the sample data

The sample data is this:

--
-- Table structure for table `dogs`
--

CREATE TABLE IF NOT EXISTS `dogs` (
  `version_stamp` datetime NOT NULL,
  `dog_id` int(11) unsigned NOT NULL,
  `dog_name` varchar(30) DEFAULT NULL,
  `dog_color` varchar(30) DEFAULT NULL,
  PRIMARY KEY (`version_stamp`,`dog_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Dumping data for table `dogs`
--

INSERT INTO `dogs` (`version_stamp`, `dog_id`, `dog_name`, `dog_color`) VALUES
('2014-09-28 09:30:24', 19849, 'Ruediger', 'black'),
('2014-09-25 02:15:23', 19850, NULL, 'white'),
('2014-09-25 02:16:41', 19850, 'Bello', NULL),
('2014-09-26 02:15:23', 19850, NULL, 'brown'),
('2014-09-27 02:16:41', 19850, 'Dieter', NULL);

What I want, is the newest version of a row, e.g. dog row.

Say I enter the dog_id 19850 with date time stamp

2014-09-26 02:15:24

Then I want to get : Bello brown

When I use a different timestamp, say:

2099-12-12 12:12:12

I want to get

Dieter, brown

Is there a way to do this in SQL?

Answer 1

Something like this should work if you specify the dog_id and version_stamp. It's going to SELECT the top dog_name and dog_color ORDER BY the latest version_stamp. Then you roll those up based on dog_id using MAX().

Fiddle example.

SELECT
   a.dog_id
  ,MAX(a.version_stamp) AS 'Version Stamp'
  ,MAX(a.dog_name) AS 'Dog Name'
  ,MAX(a.dog_color) AS 'Dog Color'
FROM 
   (
    SELECT
      *
    FROM dogs
    WHERE version_stamp <= '2099-12-12 12:12:12'
    AND dog_id = 19850
    AND dog_name IS NOT NULL
    UNION
    SELECT
      *
    FROM dogs
    WHERE version_stamp <= '2099-12-12 12:12:12'
    AND dog_id = 19850
    AND dog_name IS NULL
    ORDER BY version_stamp DESC
    LIMIT 2 
   ) a
GROUP BY 
   a.dog_id

---

DOG_ID  VERSION STAMP   DOG NAME    DOG COLOR

19850   September, 27 2014 02:16:41+0000    Dieter  brown

Answer 2

You can use 2 simple subqueries, one for each column:

SELECT
  ( SELECT dog_name
    FROM dogs
    WHERE dog_id = p.dog_id
      AND version_stamp <= p.version_stamp
      AND dog_name IS NOT NULL
    ORDER BY version_timestamp DESC
      LIMIT 1
  ) AS dog_name,

  ( SELECT dog_color
    FROM dogs
    WHERE dog_id = p.dog_id
      AND version_stamp <= p.version_stamp
      AND dog_color IS NOT NULL
    ORDER BY version_timestamp DESC
      LIMIT 1
  ) AS dog_color 
FROM
    ( SELECT                                        -- your parameters
          19850                 AS dog_id,
          '2099-12-12 12:12:12' AS version_stamp
    ) AS p ;