mysql select with union all

Question

I got

TableA

| id | san | status |       created       |
-------------------------------------------
| 1  | 100 |   3    | 2013-11-01 19:26:20 |
| 2  | 200 |   8    | 2013-11-02 03:19:35 |
| 3  | 300 |   1    | 2013-11-03 06:13:38 |
| 4  | 100 |   2    | 2013-11-06 08:28:37 |
| 5  | 100 |   4    | 2013-11-27 19:00:00 |
| 6  | 200 |   1    | 2013-11-27 19:16:22 |
| 7  | 200 |   3    | 2013-11-27 19:33:33 |
| 8  | 300 |   5    | 2013-11-27 19:50:29 |

TableB

| san | san-name |
------------------
| 100 |   xxx1   |
| 200 |   xxx2   |
| 300 |   xxx3   |

with this query (using union all because i have tons of rows)

SELECT id, max(lastdate) AS lastdate, max(san) AS san
FROM
    (SELECT `san` AS id,
            `created` AS lastdate,
            '' AS san
     FROM `TableA` a
     UNION ALL
     SELECT `san` AS id,
            cast(null as datetime) AS lastdate,
            `san-name` AS san
     FROM `TableB` b
    ) sq
GROUP BY id 
ORDER BY san ASC

i get this result (everything works perfect)

| id  |      lastdate       |   san   |
--------------------------------------
| 100 | 2013-11-27 19:00:00 |   xxx1  |
| 200 | 2013-11-27 19:33:33 |   xxx2  |
| 300 | 2013-11-27 19:50:29 |   xxx3  |

but now i want to add also the "status" of the latest "created" "id" into my result.

from TableA i want the rows ( see <- LATEST SAN ..... )

| id | san | status |       created       |
-------------------------------------------
| 1  | 100 |   3    | 2013-11-01 19:26:20 |
| 2  | 200 |   8    | 2013-11-02 03:19:35 |
| 3  | 300 |   1    | 2013-11-03 06:13:38 |
| 4  | 100 |   2    | 2013-11-06 08:28:37 |
| 5  | 100 |   4    | 2013-11-27 19:00:00 | <- LATEST SAN 100
| 6  | 200 |   1    | 2013-11-27 19:16:22 |
| 7  | 200 |   3    | 2013-11-27 19:33:33 | <- LATEST SAN 200
| 8  | 300 |   5    | 2013-11-27 19:50:29 | <- LATEST SAN 300

and it should look like this:

| id  | status |      lastdate       |   san   |
------------------------------------------------
| 100 |    4   | 2013-11-27 19:00:00 |   xxx1  |
| 200 |    3   | 2013-11-27 19:33:33 |   xxx2  |
| 300 |    5   | 2013-11-27 19:50:29 |   xxx3  |

i tried it with this code

SELECT id, status, max(lastdate) AS lastdate, max(san) AS san
FROM
    (SELECT `san` AS id,
            `created` AS lastdate,
            '' AS san,
            status AS status
     FROM `TableA` a
     UNION ALL
     SELECT `san` AS id,
            cast(null as datetime) AS lastdate,
            `san-name` AS san,
            '' AS status
     FROM `TableB` b
    ) sq
GROUP BY id 
ORDER BY san ASC

but it gives me this (WRONG RESULT)

| id  | status |      lastdate       |   san   |
------------------------------------------------
| 100 |    3   | 2013-11-27 19:00:00 |   xxx1  |
| 200 |    8   | 2013-11-27 19:33:33 |   xxx2  |
| 300 |    1   | 2013-11-27 19:50:29 |   xxx3  |

and not the right one like this

| id  | status |      lastdate       |   san   |
------------------------------------------------
| 100 |    4   | 2013-11-27 19:00:00 |   xxx1  |
| 200 |    3   | 2013-11-27 19:33:33 |   xxx2  |
| 300 |    5   | 2013-11-27 19:50:29 |   xxx3  |

could somebody help me? :o)

i created a sqlfiddle

best regards

bernte

Answer 1

I would try with this query:

SELECT tA.san AS id, tA.status, tA.created AS lastdate, tB.`san-name`
FROM
  tableA tA INNER JOIN (SELECT san, MAX(created) AS max_created
                        FROM tableA
                        GROUP BY san) m
  ON tA.san=m.san AND tA.created=m.max_created
  INNER JOIN tableB tB
  ON tA.san=tB.san

Please see fiddle here.

Edit

If you need to return all records from tableB, and only the records that match you need to use a RIGHT JOIN (which is a little uncommon) or we can swap the order of the tables joined and use a LEFT JOIN, like this:

SELECT tB.san AS id, tA.status, tA.created AS lastdate, tB.`san-name`
FROM
  tableB tB LEFT JOIN
  (SELECT san, MAX(created) AS max_created
   FROM tableA
   GROUP BY san) m
  ON tB.san=m.san
  LEFT JOIN TableA tA
  ON tA.san=m.san AND tA.created=m.max_created

Fiddle is here.