Question

我的表格看起来像这样：

| id | user | data |
--------------------
| 1  |  11  | aaa1 |
| 2  |  11  | aaa2 |
| 3  |  11  | aaa3 |
| 4  |  22  | aaa4 |
| 5  |  33  | aaa5 |
| 6  |  33  | aaa6 |
| 7  |  44  | aaa7 |

我想选择包含所有数据的所有行，并且我希望每max id添加user的数据，如下所示：

| id | user | data | f_id | f_data |
------------------------------------
| 1  |  11  | aaa1 |   3  |  aaa3  |
| 2  |  11  | aaa2 |   3  |  aaa3  |
| 3  |  11  | aaa3 |   3  |  aaa3  |
| 4  |  22  | aaa4 |   4  |  aaa4  |
| 5  |  33  | aaa5 |   6  |  aaa6  |
| 6  |  33  | aaa6 |   6  |  aaa6  |
| 7  |  44  | aaa7 |   7  |  aaa7  |

这是我的查询尝试：

SELECT  t1.*, t2.id AS f_id, t2.data AS f_data
        FROM table1 t1
        LEFT JOIN table1 t2
             ON t1.user=(SELECT MAX(t2.id)
                         FROM table1 t2
                         WHERE t2.user = t1.user )

更新所有答案都是正确的，但是当我在80K +行的表上运行查询时，MySQL需要大量时间来执行查询。对于我的项目，我将添加ajax，以便用户可以点击它，php将执行每次点击一行的查询。

Answer 1

<强> SQL Fiddle Demo

SELECT  t1.*, 
        t2.id AS f_id, 
        t2.data AS f_data
FROM table1 t1
JOIN table1 t2
  ON t1.user = t2.user
 AND t2.id = (SELECT MAX(t2.id)
              FROM table1 t3
              WHERE t3.user = t1.user)

Answer 2

这样就可以了。

SELECT  t1.*, t3.id AS f_id, concat(SUBSTRING(t1.data, 1, CHAR_LENGTH(t1.data)-1),t3.id) AS f_data
        FROM table1 t1
        INNER JOIN (select max(t2.id) as id, t2.user as userid from table1 t2 group by t2.user) t3
        on t3.userid = t1.user

Sqlfiddle：http://sqlfiddle.com/#!9/a24413/7

Answer 3

你可以使用你的逻辑来解决这个问题。只需要解决一些问题：

SELECT t1.*, t2max.id AS f_id, t2max.data AS f_data
FROM table1 t1 JOIN
     table1 t2max
     ON t1.user = t2max.user AND
        t2max.id = (SELECT MAX(t2.id)
                    FROM table1 t2
                    WHERE t2.user = t1.user
                   );

变化是：

您需要在FROM子句中为用户提供两个表之间的条件。
子查询需要加入id而不是user。

MySQL选择每个id具有最新值的所有行

3 个答案: