mysql选择与联合所有

我得到

表

| 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 |

表B

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

使用此查询（使用union all，因为我有很多行）

我得到了这个结果（一切都很完美）

但现在我还想将最新“创建的”id的“状态”添加到我的结果中。

---

从表A中，我需要行（请参见我将尝试此查询：

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

请看小提琴

编辑

如果需要返回tableB中的所有记录，并且只返回匹配的记录，则需要使用右连接（这有点不常见），或者我们可以交换连接的表的顺序并使用左连接，如下所示：

| 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  |

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是。

hi..谢谢你的评论！我稍后会在我的服务器上尝试此功能。希望你的代码速度快：D与我的旧代码相比，耗时30秒..因此我不得不选择unionall@bernte我希望它是正确的，并且和联合查询一样快：）如果是，它也应该更容易阅读！如果速度太慢，我会尝试在两个表的san列上添加索引，也会在created列上添加索引。@bernte我会尝试使用组合索引

在tableA（san，created）上创建索引idx1并使用
在表B（san）上创建唯一索引idx2@bernte那么你需要右连接或左连接。。。请看我更新的答案@伯恩特：谢谢是的索引应该是相同的。。。也许您可以尝试在tableA（san）上使用两个单独的索引
创建索引idxA1，而不是单个idx1和
在表A上创建索引idxA2（已创建）但是很难说哪一个比另一个快。。。不能确定，但是你已经拥有的索引应该更好！
| 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  |

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

| 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  |

| 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  |

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

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